Hi@meijer, I can dig into it more if needed, but I don't believe it's possible to return a 202 header with the Data Streaming service in FME Server.That service is meant to always return a data file of some sort, so would normally only ever return a 200 code on success.

If using a different service in FME Server is an option for you, one thing you could do instead is have your SOAP service call the following FME Server REST API URL instead: /transformations/submit/< repository >/< workspace > (take a look at /fmerest/apidoc/v3/#!/transformations/submit_post_22 for details).It will run the job asynchronously and will return a 202 back to the calling application.