What the best way to implement card payment through your app or website?

Myself and a friend are in the process of building an app, we can’t figure out how to securely process transactions. We’ve discussed using PayPal API but they charge us around 2.7% per transaction which we would then have to charge the customer, is there a way around this?

We’ve seen other places charge 0% commission so we’re trying to figure it out too. The payment needs to take Apple and android pay or any debit or credit card.