Money transfer api for mobile apps?

I'm developing a flutter app, and I've come across different payment solutions such as squareup payments, paystack and stripe. However all these systems essentially require you to setup an account with their services, then you can only charge money to those accounts.

What I'm looking to do is enable monetary transfers between users on the app, and simply charge a fee on top. What are the best practises for such a system? So a callable api in the vein of Venmo, or Square Cash that I can call from code when I get the details I need.

Should I create my own backend for this? If so what should I use? (I'm primarily working in golang, but I'm flexible)

Or is there a nifty flutter plugin or API gateway that I can just use directly from the mobile client?

Solution

There are various services for doing such a thing, Usually at my firm we would have our .NET rest server get the payment request from the client, and later charging it with some service that is verified for payments at our country. Note:

You will be needing to associate with that service and there will probably be fees.
Depanding on your country, you most probably MUST NOT store the payment data on your own server unless you have a certificate for doing such a thing (security standerts etc.)
If this is a private project I would suggest researching about migrating with PayPal since you won't need to handle security and the payment would go through them.

May be helpful: paypal developers