When you are using SAP Engineering Control Center in a SAP S/4HANA Cloud, private edition environment you need to have a file repository to store files, similar like in on premise as well.
There are many alternatives how to get a file repository attached, also via partner solutions.
Make sure that the following SAP Notes are implemented in your ABAP Backend:
|2||Please use version SAP ECTR 22.214.171.124 or SAP ECTR for S4 126.96.36.199 or higher on your frontend computer.|
In your <ECTR installation>\customize\config\default.txt you will need the following settings:
Don't forget to upload the preference again via ECTR menu "Administrator → System Setup → Upload Settings to SAP System
Make sure, you have configured the BTP Document Management Service as a repository as well. Follow the steps in the article here: https://blogs.sap.com/2020/12/31/using-document-management-as-a-content-repository-with-sap-s-4-hana/
You also need to adjust the preference plm.kpro.storageCateg.default pointing to your new repository, defined in Step 6 in the article above.