Trying to make my first add-on repository and hit error when building

When I push my latest code the GitHub actions starts.
But the builder always fails at this point:

[08:51:14] INFO: Run build for ghcr.io/eynergy/ha_addons:heimdall-amd64:2.6.1 with platform linux/amd64

ERROR: invalid tag “ghcr.io/eynergy/ha_addons:heimdall-amd64:2.6.1”: invalid reference format

I tagged the repository with 2.6.1 tag, but it does not seem to be the issue.