Unable To Upgrade

I'm attempting to upgrade two sites from version 2.1.14 to 2.1.19 however when clicking upgrade I just get a box requesting tenant admin credentials. I've tried providing the credentials but it doesn't accept and upgrade the site. I've followed the manual instructions and installed the version Plumsail Helpdesk app however it doesn't install when clicking Upgrade after that.
Any help would be appreciated.

Hello Mark! I requested developers to force the update for your HelpDesk sites. I will inform you about the results.

We forced the update, please check and let me know whether the issue is resolved.

Hi Evgeniy
They have both updated.
Many Thanks for your help.