How to push to a non Samba Team member branch on gitlab ?

[Jeremy Allison]

I'm working with a new contributor here:

https://gitlab.com/samba-team/samba/-/merge_requests/2741

and want to push a modified version of their patch
that corrects some things to help them work with
us here on the Team. Pushing to their branch
helps them see what I corrected so is a very
desirable thing to do.

The gitlab page above shows their branch name as:

vporpo/samba:master

and clicking the "copy" button for this MR gives
the text string: master, which certainly doesn't
seem right as a branch name to push to.

For another Samba Team member MR normally I'd just do:

git push gitlab +HEAD:<copy name>

where <copy name> is the string copied when
I click the "copy" button on the MR. For example,

https://gitlab.com/samba-team/samba/-/merge_requests/2750

"copy" gives: dmulder/smb3_posix_ext

which would allow my changes to overlay the
changes in the MR.

But what is the magic incantation to push my changes
to this MR ?

git push gitlab +HEAD:vporpo/samba:master

fails, as does:

git push gitlab +HEAD:vporpo:master

I can't see any logic or patterns in this, or am I just
missing something about git (again).

Jeremy.