We somehow managed to make it work, can’t exactly remember the details but I think at some point it involved us sending them desperate emails (or maybe phone calls, can’t remember exactly) asking them to please change some settings on their side of things so that we would be able to test as close as possible to “live”, it took them at least two or three days if not more to make the change, which created unwanted dead time for us.

To say nothing of the fact that at some point we spent at least two days practically hitting a wall over and over again: we were sending the requests exactly as their not-so-great docs were telling us to do but the response was totally different from what we were expecting. In desperation we somehow managed to contact them (meaning my boss sitting on a phone call with them) to realize that the dev instance they had provided us with still needed some small change on their side of things. Totally non-transparent framework and it all seemed as fickle as a castle made out of sand.

For comparison we had the best experience implementing Stripe, it was like night and day compared to Vantiv. Unfortunately at the end of the day you need to implement what the stakeholders want.