In documentation, we currently see :
List of tags to use for
BRANCH_NAMEis available at https://gitlab.e.foundation/e/os/releases/-/tags.
But the link currently go to nowhere…
.
Did you tried :
repo init -u https://gitlab.e.foundation/e/os/releases.git -b refs/tags/v4.0-a16
or simply :
repo init -u https://gitlab.e.foundation/e/os/releases.git -b v4.0-a16