Harmont docs
ApiErrors

user_name_invalid

Display name must be between 1 and 255 characters.

HTTP status422
typeinvalid_request
codeuser_name_invalid
Default messageDisplay name must be between 1 and 255 characters.

When this happens

You tried to set a display name that is empty or longer than 255 characters.

How to fix it

Send a display name with 1 to 255 characters and try again.

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