Cant access Nextcloud from internal and external at the same time

I currently run nextcloud version 31.0.6
I am doing so on a truenas scale server running a default installation package provided by truenas

i am unsing connector version App Version: v9.0.3 Version: v1.0.18 also provided by truenas

I am using nginx proxy manager and can connect to the only office via nextcloud from the https address just fine.

but internally i get the 403 error?

How do i solve this?

I have heard something about this thing called dns splitting but i dont have the slightest clue of what these people are talking about.

Is dns splitting the same as forwading or something i dont know. HOw do i do this,

I know its possible but no one really shows how to do they only seem to brag about the fact that they have.

please reply layman, thank you so much