Cause
The external_id in the path does not match the format: 1 to 128 ASCII characters starting with a letter or digit (Communications allows . _ : -, Surveys allows . _ -).
What to do
Use a stable identifier with that alphabet.
application/problem+json
{
"type": "https://masnet.com/developers/errors/invalid_external_id",
"title": "Invalid external identity",
"status": 400,
"detail": "...",
"code": "invalid_external_id",
"correlation_id": "..."
}