[Joe8Bit]

A good point, and may help in this case, but often when onboarding with a payment processor (especially at the 5-10m a month level of the OP) the majority of the time/complexity isn’t the technical integration.

The complexity is usually compliance (eg KYB, sanctions checks, AML) and while payment processors have done a lot to reduce the time and complexity it can still be a long and painful process.

In my experience (I’m CTO at a payment network) technical integration is <10% the time for a merchant doing this kind of volume moving processors.

Finally, what you described has happened. A lot of payment processors have been heavily influenced by Stripe’s DX and align relatively closely, or at least closely enough to make transition easier. The challenge is that few even medium sized merchants just use the core ‘move money’ APIs that are ‘easily’ replaceable, they use things like reporting/reconciliation, anti-fraud and a host of other products that make up an ‘ecosystem’ of products that in combination is very hard to replace quickly.