Cannot connect to Helm Files through Nextcloud

I’m trying to set up Helm Files but I can’t log in through the Nextcloud client. I see this error:
Timeout while trying to connect to Nextcloud at https://files.mydomain.com:9443/status.php

My helm is plugged into my router which is plugged into another router provided by my ISP. I followed the instructions on https://support.thehelm.com/hc/en-us/articles/360020232694-Setting-up-Files and enabled port forwarding for 9443 on both routers.

My Helm app says Files is turned on, reachable, and configured.
A friend pinged files.mydomain.com from outside my home and saw the right IP.
The 9443 port is open according to some random port checker website.

From the Nextcloud client I clicked login then entered the address as shown in the Helm app:
https://files.mydomain.com:9443. I also tried every variation of this I could think of, some giving different errors.

I’m totally lost here, I can’t even tell if it’s a networking issue or a Helm configuration issue. Any help would be greatly appreciated.

Hi there -

You’ll need to confirm your router support NAT hairpinning/loopback. That should resolve the issue once enabled.

Thanks!

NAT Loopback was the issue. Unfortunately my router does not support NAT loopback and is not supported by third party software like DD-WRT.

The good news is that I already have a Pi Hole as a local DNS server so it was relatively easy to set it up to point files.mydomain.com to my Helm.