Executing REST Task returns 403 error

Summary:

Hi,
We are trying to execute a Fusion REST api call from the OCI Data Integration service. We have made a REST task for this, and put in a REST api endpoint which we can succesfully execute from SOAP ui. In the REST task we don't provide authentication, but instead we add an Authorization header with our credentials in it in base64. The same request with the same authorization returns a succesfull response in SOAP ui, but always returns 403 forbidden in the Data Integration REST task. Are we missing something in how the REST tasks work in Data Integration?