In this case I would review the API docs from ServiceNow. This sounds like the payload is not correct for ServiceNow API call in order to generate the correct information in the RITM. I would also look at the Catalog item you are calling and verify the ServiceNow Workflow that is being triggered to generate the RITM. You will want to ensure that the RITM creation workflow that is being triggered is configured based on your companies requirements.
When it comes to work with ServiceNow with ISC 90% of the work is done on the ServiceNow side. So ensuring your targeting the correct end points and configured payloads are correct will are critical when using API’s to interact with ServiceNow.
I would ask the ServiceNow team to turn on logging for you user that is making the API call. This way you can see what the error message is that your getting when sending the api or if their is a 200 response but the workflow failed.
Hope this helps.