Integrating 3PL REST API with SAP Public Cloud (1ZQ Scope Item) Without Integration Suite

[mbesli]

Hi SAP Community,

We are currently working on a customer implementation in the SAP S/4HANA Public Cloud and facing an integration challenge with a 3rd Party Logistics (3PL) provider.

The customer has activated scope item 1ZQ - Third-Party Logistics (3PL) Integration. However, they do not have access to SAP Integration Suite (BTP) or any middleware in between.

The 3PL partner only provides a REST API, whereas the standard SAP 1ZQ process seems to expect SOAP-based integration (via WSDL, etc.). Moreover, the 3PL API structure does not match the expected data structures in SAP's standard outbound/inbound interfaces — meaning we need field-level and structure-level mapping.

Since we're working strictly within the boundaries of the SAP S/4HANA Public Cloud, we cannot implement classical ABAP enhancements or use custom middleware-based transformations.

Key Questions:
How can I map and transform the REST API payloads to match SAP’s expected SOAP message structure within the Public Cloud?

Is there any workaround or best practice to enable a transformation layer (without Integration Suite)?

Can we implement REST-to-SOAP mediation via custom communication arrangements or service consumption models?

Has anyone dealt with 3PL integrations in Public Cloud where the partner system only supported REST, and not SOAP?

Any guidance, experience, or documentation references would be highly appreciated.
Thanks in advance!