REST API CustomField/{fieldId}/option - 500 Internal Server Error

[Markus Mairitsch]

REST API call https://{organization}.atlassian.net/rest/api/3/customField/10115/option returns 

Response

{ "errorMessages": [ "Internal server error" ], "errors": {} }

Permission

Checked permissions by using Site & Org Admin account to create API token. See response. Cross-checked with an base user (insufficient permissions) and got:

{
   "errorMessages": [
       "Field 10115 does not exist or you don't have permission to view it."
   ],
   "errors": {}
}

Creation

The custom field & select list options were created via Cloud Web Page and not a Connect App.

Thanks for your help!