The problem with their APIs is that they're broken and/or stupid in surprising ways the moment you look beyond the most basic things. An example: the REST API

The problem with their APIs is that they're broken and/or stupid in surprising ways the moment you look beyond the most basic things. An example: the REST API allows you to create a billing agreement. You can make the customer approve it by redirecting them to the appropriate place, and then execute it to start the cash flow. Obviously, it takes an agreement ID to do anything with it after creating it, so it would make sense if creating the agreement gave you an ID, right? Well, it doesn't. When I wrestled with it a few years ago, there was already a few-years-old bug on their github about it, and the workaround was to extract the part of the approval URL which contained the EC-token. If you sent that part of the URL later to /agreement-execute, it would set things in motion... and return you the actual ID you wanted in the first place. I just checked the docs and it still hasn't been fixed, but at least they're self aware now and the documentation actually tells you to use the EC-token as a temporary agreement ID until you get a proper one. I'm not sure if documenting a hack is something I prefer to fixing a bug; at this point I'm just happy I don't have to work with this pile of crap anymore. The issues with billing agreements just never stopped. Another one we faced had to do with the agreement start date – the documentation said that the datetime needs to be in the future, which makes sense. "5 minutes from now" worked in testing. But then every now and then there would be a customer for whom the error would come up again. After bringing the issue up with paypal support (let's just say that the level of their english matches the quality of the REST API), we eventually deduced that paypal takes the agreement start time and adjusts it according to the users's timezone – therefore sometimes it would "roll back the time" before the current datetime (which of course wasn't timezone-compensated). Where do they take this timezone data from? Who knows; not from the API call inputs, that's for sure – nice, functional design. There were more like these and I could go on and on; eventually we shut down all the paypal integrations except for the simpliest, one-time payments, and pushed the paypal payment option very far in the payment interface, hoping that most of our customers won't find it too easily and will just use Stripe instead.