Nice article, and I would say only one on internet. I am doing this right now, and cannot believe how complicated it is, wouldn't expect this from google tbh. Anyhow one question for you:

When you say "Subsequently, we compiled an alpha build and submitted the application for bank review. For this, we provided access to test data so that bank employees could go through specific steps."

What is "test data" here, I cannot figure out part where if google didn't approve everything, then users would need to test in sandbox env no?