I have been testing out the GetMyMessages and GetMemberMessages APIs from the sandbox and have had no success getting GetMyMessages to return any messages. Then I tried to send/receive messages between a couple TESTUSER_ users in the sandbox, but the My Messages tab Inbox and Sent sections are always empty, despite sending messages between the two users, using multiple methods such as "Contact User" (tried both with and without an associated Item) and Ask a Question section for a listed item. I receive emails when a message is received by one of my test users, but it never shows up in the My Messages inbox. If the recipient responds to the message, it says it was sent and will show up in the Sent box, but again, that box is empty.
I tested the exact same thing between 2 actual users on the live eBay site and the messages showed up in the Messages Inbox and Sent box immediately.
Am I doing something wrong in the Sandbox? As anyone else seen this issue? Until I figure this out, I'm unable to integrate (and test) the GetMyMessages operation on my site.
P.S.: GetMemberMessages seems to be working correctly, it will return all questions asked via the sandbox, but there is data and usecases in GetMyMessages that I need that GetMemberMessages doesn't have.