I can't access HomeAssistant from outside: error NSURLErrorDomain -1200

Hi everyone, i set up HomeAssistant with NGINX and DuckDNS: i opened port 443 with port forwarding on my router and i can access my HA istance with my duckdns link… up until yesterday.
Now i can connect via browser and get the “this website is not secure” alert, but i can’t access it through the app because i get the NSURLErrorDomain -1200 error.
I get it’s an SSL certificates error, but why? And how i can i solve it?
I even tried to switch to DynuDNS but with no success, i can’t reach my istance, in the same conditions, even with the “this website is not secure” error

PLUS: Why does my companion app connects to ha through the external link and not the internal one?