Strange Internet Connection Error Just By One App Only

Hello folks, I have a unique issue with my home internet. Everything connected to my home internet works, except one unique situation.

I have an app I bought and activated. After about two uses, I would not be able to use it again, it will ask me to re-activate it. When I report to the app maker, they even reset the app, which will sometimes work and back to the old issue. I was sent a new activation code which will not activate at all. So, in my process of elimination of possible issue, I created a table to illustrate what I went through to pinpoint where the issue might be coming from. I cannot activate from my home network system. Activation worked with an open public WiFi and at my ISPs office, with their WiFi.

I am thinking there has to be something with my router that is preventing the app from getting internet connection to activate. Why so if at an initial state, it activated, but not now. But again, connected directly to the modem (from ISP) does not work either. So, the issue would be from ISPs outside line through my home network.

Please, any suggestions?
Cheers

Your app's vendor should disclose what DNS host address they're trying to connect to, and on which network port.

It may be your home network is blocking this connection, and therefore the app never completes activation. This could be caused by an improper firewall setting or bad network routing from your home ISP connection to the vendor's server.

You could test this by running a PowerShell command to open a network connection on that port.
powershell Test-NetConnection google.com -port 80

garlin said:

Your app's vendor should disclose what DNS host address they're trying to connect to, and on which network port.

It may be your home network is blocking this connection, and therefore the app never completes activation. This could be caused by an improper firewall setting or bad network routing from your home ISP connection to the vendor's server.

You could test this by running a PowerShell command to open a network connection on that port.
powershell Test-NetConnection google.com -port 80

Hello, I got the info from the app vendor. Instead of the "google.com" it has the vendor's.

Now, in Powershell, after running the as a test, to open the port, what else? What am I looking for? Please, a little more details for me, please.
Cheers.

Any reason why you haven't mentioned the name of the app or provided the info asked for by @Samuria?

UPDATE

Through process of eliminations, I suspected the ISPs modem would be the culprit. The modem comes with inbuilt router, which got disabled by the ISP, so I can use my own router. When I got it enabled, used it, same issue. I got another modem, just in case the modem has issue. Luckily, they have a new modem without the built-in router. Took that home, connected, the app was able to activate. The issue was in the modem/router combo from the ISP. Very strange indeed.

Thanks everyone for all your help. Well appreciated!
Cheers.