Hello, we've built a system which can support several different coins and it currently works with BTC, LTC, ETH, USDt. We can include some other ERC-20 tokens if you require.
Front end: iOS and Andoid apps for users.
We also have an online payment gateway ready, which tracks blockchain payments.
And we have infrastructure ready for this project: redundand servers with full coin blockchains in several different locations to facilitate payment and invoicing procedures.
We've been working in this field for many years and ready to provide you with the stable and reliable solution.