Cannot withdraw from keybase account: mysterious (and misspelled) error message

I'm playing around with the keybase app on Android, particularly the "wallet" bit. I don't mind saying I have no idea what I'm doing, and don't understand StellarX at all.

In any case, I've somehow managed to get $5 into my keybase account, and figured that if I clicked the "withdraw" button I might be able to transfer it to my bank or something. So I tapped that button, and saw a page that says nothing but
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challenge post didn't reutrn OK/200
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I don't know much about cryptocurrency, but if _I_ were making an app that intends to handle money for people, _I_ would ensure that the error messages were actually informative, and were spell-checked.

This does not instill confidence.

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I'm using version 4.6.0 of the app on a Pixel 3 running an up-to-date version of Android 10.

Start by reproducing the withdrawal flow on the reported Android 10 and app version 4.6.0 setup, then trace the response that produces “challenge post didn't reutrn OK/200.” No files or tests are named; done means the withdrawal failure is explained with an informative, correctly spelled error message.

Written by the indexing model from the issue text.