Trouble with port 80 and Let's Encrypt

[RenzoS]

Hello all!

I'm having trouble with Let's Encrypt and port 80 on my Asustor AS1002T v2.
On the settings > general panel, I have HTTP (8000) and HTTPS (8002) enabled.
At services > web server I have the server enabled with HTTP port 80.
In my router, I've checked for open ports, and port 80 is open.
I also created a new forward to be sure that the port is opened for the NAS.

At settings > manual connect I activated the EZ router option.
I also enabled UPnP on the router.
Here I've added a forward for Web Service, NAS port 80, Router port 80, TCP. Status appears to be disabled.
I'm creating an certificate in settings > certificate manager.
I've selected Create certificate from Let's Encrypt.
For the domain name, I've tried putting in my WAN-IP and the EZ-Connect URL.
For E-Mail ofcourse my own mail.
Selected update automatically when certificates expire and clicked the Finish button.

The message Unable to apply settings. Please try again. (Ref. 5401) appears.
I tried contacting my ISP but they don't give support on port forwarding.

Unable to apply settings. Please try again. (Ref. 5401)

I don't know what to do now...
I'd appreciate your help!

[orion]

Did you try to connect to your NAS (using your domain name on port 80) outside your home / office? If you cannot see your web page, there should be problems on your port forwarding settings. Some ISP might block 80 port.

[RenzoS]

Thanks for your reply, Orion.

Yes, when I try to connect with my NAS from another network it just does the job.
It automatically changes the port to 8002 as I configured HTTPS, and this is the port I've set at the General settings.

[RenzoS]

When I use ping.eu, and I type my WAN and port 80, it says that the port is open, so I guess the problem is in the NAS...

[orion]

Oops, that's ADM web page. You should enable Services -> Web Server. And you should set web server port to 80. (ADM web site should apply to other port number.)