Error message from Dataverse API endpoint for sending metadata to a PID provider can be misleading

[jggautier]

What steps does it take to reproduce the issue?

• When does this issue occur?
  When using the the API endpoint for sending metadata to a PID provider like DataCite, and including a persistentId that doesn't exist in the Dataverse installation, such as:
  curl -H "X-Dataverse-key: $API_TOKEN" -X POST "https://$SERVER/api/datasets/:persistentId/modifyRegistrationMetadata/?persistentId=doi:10.7910/DVN/12345"

• Which page(s) does it occurs on?
  The confusion can occur where a user sees what the endpoint returns, like in the terminal or IDE they used to call the API endpoint

• What happens?
  When using the the API endpoint and providing a persistentId for the query parameter, if the PID doesn't exist in the Dataverse installation, the endpoint returns an error message that reads "When accessing a dataset based on Persistent ID, a persistentId query parameter must be present," even when a persistentId query parameter is present.

  This can cause confusion about the cause of the error and what the user should do next, since the problem isn't that the persistentId query parameter isn't present, but that the persistent ID doesn't exist in the Dataverse installation.

• To whom does it occur (all users, curators, superusers)?
  Superusers

• What did you expect to happen?
  The error message would let the user know what caused the error so that they can at least infer how to fix it.

  When the persistentId is something like doi:12345, the endpoint returns "Bad dataset ID number: doi:12345," which I think is a less confusing error message. Could that message be used?

  Why does the endpoint return a "bad dataset ID number" message when the persistentId is doi:12345 and a "persistentId query parameter must be present" message when the persistentId is doi:10.7910/DVN/12345? Both persistentIds do not exist. Did we tell Dataverse to check only the format of the given persistentId?

Which version of Dataverse are you using?
v6.9

Any related open or closed issues to this bug report?
I couldn't find any directly related to this API endpoint's error message

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