"Call Service" Node error without log when trying to get a camera snapshot

[finite coyote]

I try to retrieve a screenshot of a camera. the camera exists and shots images.

But somehow when trying to call the service as shown, the node itself shows an error, but there is no log output in either the debug box inside node-red ui or inside the docker logs.
The filepath exists and is writeable from within the docker.

Any ideas how to debug this?

[lofty pawn]

The 'Data' seems to be in Jsonata rather than Json, what happens if you click on the down arrow and select {} JSON rather than J: expression?