I'd like to incorporate a payment gateway into flutter web. Payment UI is loaded in flutter web, but I'm not sure how to get callbacks from it.

I've done web API work with PayPal for shopping carts and subscriptions; it was a complicated API, but it was well documented. (This is something you'd expect from third-party digital banking tools.) I'm sure this will be a major undertaking. You could use Webviews from a web app instead, which would be much easier.

I also have a lot of experience with the PayPal API, but I also have experience with Braintree's API, which is on a whole different level, as it is designed for you to directly store credit card and customer information in your own database. As mentioned, Stripe is a competitor to Braintree, although Braintree is owned by PayPal.

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