Transaction Features for HTTP and SAP-XML
When executing HTTP Posts using IDoc-XML and XRFC with transactions, you should make sure that your client correctly handles such calls. It should have transaction management that supports at least the following features:

Transaction ID generation.

Resending documents with same transaction ID in error cases.

After a successful execution of a transaction, a document cannot be sent again.
To transfer the transaction ID to Adapter for SAP, you add an extra header to the HTTP POST, x-tid, that contains the transaction ID.