HP Printer Wireless Set up Issue

I agree with Cali Cat the message is probably just not exactly what is going on. The printer is pretty old but it was working on your prior network device. It could be you hard set the IP address on the printer previously so be sure to check the actual IP address the printer is trying to use. If it has a static IP address change the IP address to DHCP so it obtains an IP address from the T-Mobile gateway. It could be the printer logic with the IP address on an incorrect network subnet will report that error though it is not the proper message to report. I could see from the user setup info that it will need WPA so it is too old for WPA2 or WPA3 authentication. It would also probably only work with 2.4 GHz and not 5 GHz frequencies so just make sure the 2.4 GHz also has WPA for authentication.