Issues with WIFI printing from Brother HLL8360CDW printer - HELP (please)!

I have two iMac computers operating on Cataline 10.15.7.  The main computer is connected to the printer via a WIFI network, and the secondary one is also connected to the same WIFI network. The printer is only connected to both computers via WIFI; there is no USB cord connected to either computer. Both computers are on a 2.4 Ghz network (the preferred type of network indicated in the Brother setup information).

When I try to print from the secondary computer, the computer sends the print command to the printer, but then a message window appears saying “Waiting for authentication”. I have tried a number of passwords including one for accessing the main computer, one for accessing the secondary computer, and one for accessing the network to which both computers are logged in. I would have thought that one of these passwords would have worked, but no - so I have no idea what is meant by "authentication". The printer prints documents from the main computer without a “Waiting for authentication” message. 

Brother printer drivers are installed on each computer, and the printer is listed in the printer list for both computers. The printer is only a printer - no fax, no scan functions. 

I am hoping that someone has a fix for this issue which is slowly driving me around the bend ... and it's not a long drive! 😬