Is your peer’s endpoint, hj82918.glddns.com:51820 a different GL device @ a remote location, hence its name, Home IP?
If so you may need to setup a port forward to it, to the WG Server device, to allow :51820 to ‘flow through’ if it’s behind another router or a ISP modem that has router-like functionality. I’m assuming Home IP has a WG Server running on it, of course.
Ideally you want the ISP’s modem to be just that, a modem, not a Wi-Fi access point or router itself. Depending on the model it could be a matter of putting the GL device on the ‘DMZ’ but its best to set the modem to ‘bridged mode’ if it’s possible.
It’d also be helpful to check a DDNS Test, just to be sure: