Created a kernel and gadget snaps successfully then building an ubuntu core image here it was showing this error. I just created .json model file for this image creation then Signed model assertion with my key using the below command $ cat eragon-model.json | snap sign -k default &> eragon.model
This command has been created a eragon.model file then I tried to build my board image using $ sudo /snap/bin/ubuntu-image -c devmode -o eragon410-SDtest.img eragon.model, here it was showing an error.
Does anybody know the solution.