I merged a branch, but when I try to tag the merge commit I get "failed to resolve" error.

[Paul]

I created a pull request, and assigned two other developers as reviewers. I merged the pull request prior to their approving the pull request. I know - got ahead of myself. One of the other developers has clicked on approve, but not the other. The merged commit shows up in the master branch as a "dimmed" object. I cannot tag that commit nor any other commit after the pull request. Is this a matter of getting the other developer to approve the pull request?

Update

This is the command line:

PS C:\Users\paulo\projects\eximis\softwaredocuments> git tag -a XCORSOFTWARE-20190331-BL_DEV_IDE_PROJ_RENAME -m "Rename
the MPLABX IDE projects so that they are more similar" b8bacf6
fatal: Failed to resolve 'b8bacf6' as a valid ref.
PS C:\Users\paulo\projects\eximis\softwaredocuments>

This is the commit. Everyone has approved the pull request at this point.

Thanks,

Paul E Ourada