Note that I have tried the hubspot_owner_id as an integer (no quotes) and as a string (with quotes) and I get the same error response. I have confirmed the stage and pipeline name.
Error Response:
{"status":"error","message":"Property values were not valid: [{\"isValid\":false,\"message\":\"8386379 was not a valid owner ID\",\"error\":\"INVALID_OWNER_ID\",\"name\":\"hubspot_owner_id\"}]","correlationId":"716f8fb8-3347-47c3-b2a1-8aee1ab5bea5","category":"VALIDATION_ERROR"}
My app has the 'tickets' scope. I have submitted the same create POST request without the hubspot_owner_id and the ticket is created successfully, so I know my OAUTH routines are working.