Cannot connect a Facebook Portal Mini to my AT&T router

I have tried to connect 2 different Facebook Portal Minis to my household AT&T network.  We are on fiber with a fast connection and an AT&T-furnished router.  I can get as far as entering my password, and a checkmark appears next to the name of my network (the 2.4 GHz band) to show that we are connected.  Then the Portal tries to update its software and I get a message "No Network Connection."  I cannot get past this message.  Facebook tech support could not help and AT&T will not connect me to a live person.  I do not have this problem with any other piece of hardware!  Has anyone else experienced this and do you have a solution?  Help!