Running a BPA from a REST API

Hello everyone,
To run a BPA from an API, I have been using this URL for a while:

main/ifsapplications/projection/engine-rest/process-definition/key/BPA_NAME/start

And in the body of the API, I pass it the property:

“withVariablesInReturn”: true

This allows me to directly retrieve all the variables used in the workflow in the API return.
However, I have noticed that this no longer works beyond SU6 in 25R1.

Have you encountered this issue?
Thank you.
Theo