422
invalid_reasonplatformThe reason is not one of the allowed reason codes
Returned by the implementation; no specification rule declares it yet.
Some actions take a reason that must be one of a fixed list of codes, so the audit trail can be searched and counted. This one was not on the list. errors[0].field is reason, and details.allowed carries the codes the action accepts.
A blank reason is a different error: see a reason is required.
Why the API refuses
the reason must be one of the allowed reason codes
What to do
Send one of the codes in details.allowed. If none of them fits, use the generic "other" code and put the specifics in the free-text reason rather than inventing a code.