We have updated the documentation for the /transfers endpoint in regards to our error codes. Previously, only 400 error returns were documented. However, many of our errors actually came back as 422 and we are standardizing on this in general. We also document 404 as a response if the account is simply not found. For any other issues which prevent us from attempting the transfer (whether the account is inactive, has transfers disabled, insufficient funds, or has otherwise exceeded its limits), we will return a 422.