A few years ago a client who sold printer ink on eBay and Amazon wanted to branch out to another store, so I grudgingly began to implement the new API, I followed all the API docs but no matter what, I couldn’t get it to work, eventually I contacted their support and was told it should work. Turns out the test API was faulty and that they had no interest in fixing it instead suggested we tried test data on their live account. I refused and for once the PM agreed with me and went back to the client saying the problem was the retailer.