Your repository name must be in lowercase 
This error is not super descriptive but all it means is that docker repository names must be in lower case.
If your image is myregistry.com/myimage:latest myregistry.com is the repository, myimage is the image name and latest is the tag or version. If no / exists in your image name like nginx:latest it means that its stored in the default docker registry hub.docker.com.
If your image name is something like this DEV/myimage:latest it’s invalid, since DEV (your repo name) is not in lower case. dev/myimage:latest is valid tho.