Error codes
invalid_inbox_username
HTTP status: 422
What happened
The inbox username is empty, too long, uses characters that are not allowed, or is a reserved role name. Usernames are 1 to 64 characters and use lowercase letters, digits, dots, underscores or hyphens. They cannot start or end with a dot or contain two dots in a row.
Reserved names include postmaster, abuse, admin and noreply.
How to fix
Choose a non-reserved username that matches the rules, or omit username and let the API assign one.
Source: docs/errors/invalid_inbox_username.md.