ServiceNow - 403 Error from calls to POST /agents

Calls to the POST /agents endpoint may receive the following 403 error:

"providerMessage": "error - {detail=Error during insert of sys_user ([....]), message=Operation Failed}, status - failure"

if you receive this error, a possible reason is that the agent of the same name and email address already exists in the endpoint account; deleting the agent should allow the POST /agents endpoint to properly create a new agent.