ATT LG Mobile phone not stay connected to ATT Wi-Fi

I followed the instructions to connect my LG K30 (ATT mobile phone) to my ATT Wi-Fi but it won't stay connected. It connects and immediately disconnects.

I do not have unlimited data on my mobile phone so when I'm in the house, I want to use my wifi. I have set warning limits on my phone and am hitting it while I'm in quarantine.

How can I keep my ATT mobile phone connected to the ATT Wi-Fi?