Embedded MPC Wallets for Payments Apps on Solana

Stablecoins have emerged as a key success story in the blockchain industry. The growth in circulating supply, the variety of stablecoins available, the volume of transactions, and the range of use cases highlight how they have achieved product-market fit.

The key benefit of stablecoins over native cryptocurrency remains their stability. They are used by enterprises, financial institutions, and individuals for use cases such as payments, remittances, liquidity management, and even insurance. 

Stablecoin use on Solana has grown significantly over the last year, making it an ideal ecosystem for building payment applications. In early 2025, the total stablecoin supply on Solana surpassed $11.7 billion, with an astounding $5.7 billion increase in January alone. Trading volume has also surged, highlighting the rising demand within the ecosystem.

Today’s Stablecoin Payments Market

Although stablecoins have grown, the payments market remains nascent. While large players exist, such as Bridge (recently acquired by Stripe), no single application has captured the lion’s market share.

Instead, regional and use-case-specific apps catering to the needs of local and niche populations have shown strong growth worldwide.

From apps targeting freelancers and remote workers to regionally focused digital dollar accounts and trade-industry B2B payments, stablecoin businesses are not one-size-fits-all. 

ZAR, for example, allows merchants, starting in Pakistan, to turn cash into dollar-pegged stablecoins and spend those digital dollars via virtual and physical cards.

Grey, a global banking app for freelancers and digital nomads, allows businesses to send payments in USDC to simplify cross-border transactions, reduce fees, and reduce exchange risk.

By focusing on specific customer bases, these companies have found a specific use case in which stablecoins provide significant benefits, gain product-market fit, and slowly expand their global reach or feature set.

Stablecoins in Emerging Markets

Emerging markets have become particularly popular for new stablecoin payment apps, both B2C and B2B because the traditional financial system is often inadequate, expensive, and/or technically outdated. Companies like Yellow Card and Conduit doubled their transaction volume from 2023 to 2024.

Castle Island Ventures and Brevan Howard surveyed crypto users in emerging markets, including Brazil, Nigeria, Turkey, Indonesia, and India. They found an increased use of stablecoins for non-trading purposes, including purchasing goods and services and paying for business expenses.

This shift toward stablecoins has affected emerging financial entities, traditional banking and payment institutions in these areas, and developed economies.

Brazil, where 90% of crypto use is stablecoins, has seen the issuance of stablecoins from Mercado Libra, a popular e-commerce site, and Braza Group, a traditional player in the interbank market. PayPal, a major player in global payments, including the US, launched its own stablecoin in 2023 and expanded to Solana in May 2024. Fnality International, backed by global banks such as Santander, HSBC, Barclays, and UBS, aims to reimagine wholesale cross-border payments on stablecoin rails.

In the words of technology investment firm a16z, stablecoins are likely to “eat payments." There is no more promising environment for this takeover than a high-speed, scalable, low-cost blockchain like Solana.

The Need for Embedded Wallets to Drive User Adoption

While most crypto-native users are likely to use standalone non-custodial wallets like Phantom or Backpack, embedded wallets have grown in popularity for apps targeting an audience of users new to crypto. Embedded wallets are integrated into the app or website, significantly benefiting businesses and users.

For the business, it allows them to quickly onboard new customers without sending them to another site or app store to get started. For users, embedded wallets often have improved designs that offer security without having to understand private keys or seed phrases.

In addition, embedded wallets don’t require additional downloads, allowing for direct payments within the app.

Payment apps typically function best when they integrate embedded wallets. On the surface, these apps look like traditional fintech products but use stablecoins on the back end.

Customers don’t need to know or understand how blockchains work to receive the benefits, opening up a much larger audience to these payment apps than traditional crypto wallets.

Embedded Wallet Infrastructure for Solana

As more entrepreneurs understand the benefits stablecoins bring to the payments industry, more people will want to create their payments businesses with stablecoin infrastructure.

However, they may not have expertise in building on blockchain. That is where Wallet-as-a-Service (WaaS) solutions like Portal come in.

Portal provides the necessary infrastructure for developers who want to integrate embedded wallets and stablecoin payments into their applications without needing blockchain developers.

Portal’s suite of SDKs and APIs enables a seamless integration, providing developers with a smooth and secure experience and enabling the business to go to market faster.

One of Portal’s standout features is its use of Threshold Signature Scheme (TSS) Multi-Party Computation (MPC), which is recognized as a superior cryptographic solution for key management functionality.

With TSS MPC, an app's users maintain total control over their digital assets without managing seed phrases or handling common self-custody challenges.

The Enclave MPC API also allows companies to create a hot wallet for treasury fund management. It will enable companies to manage their internal treasuries or handle treasuries on behalf of their end users with unparalleled efficiency and security.

How TSS MPC Optimizes for Security, Usability, and Scalability

Let’s examine what makes the TSS MPC architecture a strong contender for the enterprise use case. 

Security

Shamir's Secret Sharing (SSS) MPC and TSS MPC divide a single private key into several key shares held by multiple entities. With TSS MPC, unlike with SSS MPC, these key shares are never fully reconstructed into the private key at any point. 

Keeping key shares separate from each other—whether at wallet generation or transaction authorization—reduces the possibility of collusion.

Two-of-two parallel threshold creates only two key shares and requires both to be used for every transaction, making it a highly secure option for an MPC wallet. The end user holds one key share used to sign transactions, and the wallet provider (for example, Portal) holds the other; only having two shares makes the process simpler than MPC wallet designs with three or more key shares.

Because both key holders must sign the transaction, the end user can rest assured the wallet provider holding the second primary key share can never access funds without them.

Usability

MPC wallets create and access accounts using social sign-in or biometrics rather than seed phrases. The whole process can take 30 seconds or less. Should users ever need to recover access to their accounts, backup key shares are encrypted and stored away from their device, minimizing the possibility of a bad actor gaining access to both the account on the device and the backup keys. 

The enterprise benefits from the two-of-two parallel threshold design, which reduces the number of parties to vet and set up to store keys or sign transactions. MPC wallets can also be set up with Account Abstraction, which offers gas subsidies and transaction batching features. Portal offers this capability directly in our SDK.

For more details, read our Account Abstraction documentation or blog.

Scalability

The TSS MPC design accommodates thousands or even millions of users per organization without concerns about lag or latency. TSS operations, including wallet generation, backup, and recovery, have no gas fees.

Additionally, organizations can implement flexible policies to generate new key shares with TSS MPC. For example, a business can generate a new set of key shares every time a user logs in and authenticates, or it can choose to refresh key shares only during the recovery process.

Real-world Applications of Embedded Wallets for Payments

Several innovative companies leverage Portal’s infrastructure to power their stablecoin payment solutions.

Braidpay: Stablecoin Invoicing & Payments App

Braidpay uses Portal’s cloud-native architecture to provide scalable infrastructure. Targeting freelancers, marketplaces, and other audiences that rely on individual invoicing and payment, Braidpay needed the ability to serve a large and growing global user base with secure and low-cost stablecoin transactions.

Using Portal, Braidpay has removed the complexity of gas fees, improving the experience for those new to crypto. In addition, enhanced security measures ensure safe treasury management, allowing Braidpay to confidently maintain its customers’ trust.

Bleap: Mobile-first Neobank for USDC and EUR Stablecoins

Bleap, a mobile-first neobank, offers a banking product that allows people to use stablecoins for everyday payments. Customers receive a Mastercard debit card linked to a stablecoin account (EUR, USD), from which they can spend at a 1:1 ratio while earning up to 2% cashback.

Bleap also offers global transfers with zero fees and up to 5x higher yields than traditional savings accounts via DeFi savings tools. Because it relies on Portal’s embedded wallets, customers gain complete control of their assets without learning new technical or spending patterns.

Bando — Stablecoin Payments for US-Mexico Remittance

Bando, a US-Mexico remittance service, uses Portal’s Enclave MPC APIs to implement a secure treasury management system.

Through its secure on/off ramp solution, Bando aims to transform the financial landscape in LATAM. It bridges traditional finance and crypto through a streamlined user experience that is recognizable to the local market. Portal allows Bando to quickly add new chain assets to its treasury holdings and sign transactions using multiple DeFi protocols through a simple API implementation.

How to Implement Portal’s SDKs & APIs

Portal has two products of value to Solana-based payment solutions.

Portal SDK 

The Portal SDK offers out-of-the-box Web3 connectivity for both desktop and mobile browsers. Portal offers clients Multi-Party Computation (MPC) wallets, specifically using Threshold Signature Schemes (TSS) for its embedded wallets. Specifically, Portal uses an implementation where two sets of key share pairs (parallel 2 of 2 threshold—four shares total) ensure reliable backups with fast signing.

Enclave MPC API

The Enclave MPC API offers a quick way to integrate an MPC signer into any application on Solana. Installation requires no specialized knowledge and takes only a few minutes. It runs in an AWS Nitro Enclave, providing a trusted execution environment that can only be accessed by the running application. Thus, it offers the security of MPC, the simplicity of API, and the speed of server-side compute.

Get Started with the Enclave MPC API

Sending your first transaction with Portal only takes a few minutes following our Quick Start guides.

1. Request Access

First, request access to get a free Developer account at Portal.

2. Create an API Key

All API requests require authentication via a Client API Key. 

Here’s how to create an API Key from your Portal dashboard:

• Click Settings
• Go to “Test Client API Keys”
• Click "New"
• Copy your API Key

3. Generate a Wallet

Generating a new Portal Wallet is as simple as a single API request:

curl -X POST 'https://mpc-client.portalhq.io/v1/generate' \
    -H 'Content-type: application/json' \
    -H 'Authorization: Bearer <CLIENT_API_KEY>' \
    -d '{}'

Portal Wallets have all the proper key materials to support Solana.

4. Sign a Transaction

Signing and submitting a transaction onchain is a single API request:

curl -X POST 'https://mpc-client.portalhq.io/v1/assets/send' \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer CLIENT_API_KEY>' \
  -d '{
    "share": "<SHARE>",
    "chain": "solana-devnet",
    "token": "NATIVE",
    "to": "75ZfLXXsSpycDvHTQuHnGQuYgd2ihb6Bu4viiCCQ7P4H",
    "amount": "0.0001"
  }'

Using our Send Assets endpoint simplifies the complexity of transferring native or SPL tokens: one endpoint and no need to build out complicated transactions to sign.

And that’s it!

You can build and test out your Portal Wallets in a few simple steps.

Conclusion

Builders and businesses interested in starting a payments company today are likely to find that stablecoins prove the best technology available to offer customers global, secure, fast, and cheap payments.

Once they start building, they will likely discover the need to integrate an embedded wallet to capture the largest audience possible. Infrastructure companies like Portal were designed to help these products get off the ground quickly without compromising security.