Malformed server config when i do login from outside local LAN

Hi, i have truenas core + nextcloud running great on local LAN at home. I managed to configure port forwarding for ports 80, 443 according to instruction.
Now i try to enter/login using external IP of home router, i get error message in the next cloud client which says malformed server configuration. I know there has been other thread circulating around with this error but still different than mine , that is not during login. Any help here? Thanks.,

Can you provide the server side Nextcloud log entry from one of these external login attempts? That’s what’s needed to track this down.

how do i get the log??? file location? I am new to all these.

The typical location is data/nextcloud.log in your Nextcloud instance / within your Nextcloud container.