While trying to integrate a third-party service:

Their Android SDK accepts almost anything as a UID, even floats and doubles. Which is odd, who uses those as UIDs? I pass an Integer instead. No errors. Seems like it's working. User shows up on their dashboard.

Next let's move onto using their data import API. Plug in everything just like I did on mobile. Whoa, got an error. "UIDs must be a string". What. Uh, but the SDK accepts everything with no error. Ok fine. Change both the SDK and API to return the UID as a string. No errors returned after changing the UIDs.

Check dashboard for user via UID. Uh, properties haven't been updating. Check search properties. Find out that UIDs can only be looked up as Integers. What? Why do you ask me to send it as a string via the API then? Contact support. Find out it created two distinct records with the UID, one as a string and the other as an Integer.

GFG.