See the errors under "Errors not from the spec" in InternalError.swift. Need to:

1. confirm whether the library should be throwing this error (e.g. check how JS handles it)
   • Understand rules for checking HTTP response status code #453 is a related issue
2. decide whether it's something that should be in the spec, and add if so
3. else, decide whether there's a more appropriate error code / status than 40000 / 400, to avoid violating CHA-GP5, and give them appropriate error messages
   ┆Issue is synchronized with this Jira Task by Unito