Need sample payload for Create Invoice Attachment where attachments are already uploaded to UCM

Summary:

We are trying to attach an attachment to invoice from the OIC integration. Followed the below steps.

1. Create an invoice with: /fscmRestApi/resources/11.13.18.05/invoices
2. Upload a file to UCM with the SOAP service -> uploadFileToUcm
3. Attach the file using /fscmRestApi/resources/11.13.18.05/invoices/{InvoiceId}/child/attachments

Facing issue with the 3rd step. We want to display the physical copy of the attachment at UI level not the UCM url. How to link that from UCM ?

Note: We are doing this way because file can be more than 10MB, so not going by the approach of converting the file content to base64 and then using erpObjectAttachment service to attach the physical copy.