Shotstack and integromat

I want to put a watermark on a picture on integromat so I add shotstack app alone, put in a static picture and static watermark file. I ran shotstack module alone with these 2 static photos but the message I received was always: [400] bad request: Media file could not be found or was invalid.

I checked 2 photos that I added manually and I even give the editor role

Could you share your scenario?