Unable to add shared printer from another Mac on network

I've solved my own problem. In the print queue menu, there is a tiny symbol with an arrow partly around it, which when clicked enables entry of a name and password. It autofills the name of the computer, but what's needed is the name of the account. If that is entered incorrectly, nothing happens but the screen clears, and you have to go back to the print queue and fill the boxes in again. I suggest that is a bug: a message should come up telling the user that something has been entered incorrectly.

I have ticked more boxes: I had to add my name to the user list. So now there has been communication between the computers and the printers, but from both printers I have the message "Hold for authentication". I can't see where or how I can authenticate: there is no window open, and both printers have the green idle icon against their names.

I have deleted the jobs to avoid blocking use of the printers.