subscribing of or subscribing to?

I received a Location error on a website that suggests me to try subscribing of Romania's service when within its boundaries

Basically I'm trying to subscribe to a Romanian service, but I'm not in the country, and they detected that based on IP probably, so they threw that error.

However, is the sentence correct grammatically?

It should be

try subscribing to Romania's service

Since this is HBO service, which operates in many different counties, the phrase Romaina's service is fine.

The rest is also fine. There are many ways to say that some action is not possible due to the user's location. Here is a real-world sampling, from sources whose first language is English:

We're sorry, this music playlist is only available to listen to in Canada. (source)
SBS On Demand content is only available to stream within Australia due to publishing rights (source)
We're not able to play this video in your current location. (source)
The service is not currently available in your area. Click here to access our help section. (source)
Sorry. This video is not available to watch through ITV in your region. (source)