Yes, it is normal.

At some point, we got tired of working for nothing.

We launched the subscription service two years ago to encourage users to help fund a tool they use and benefit from. Although it didn't attract a massive audience, the service allows you to keep the instance up to date through the continuous integration of fixes. We therefore decided to restrict access to the online user manual to customers subscribed to our services (whether for hosting, support, or simple update subscriptions) in the hope of generating user interest.
It seems to be working, at least this made you react.

Open source cannot survive without financial support.
You like it? Support it!