I have a subscription, but it says I do not have a valid subscription

You need to enter the Download Key in the settings of Regular Labs Extension Manager.

You can find the settings by clicking on the Settings button in the Regular Labs Extension Manager component.

You can find your download key in your Downloads overview (after logging in).

I get the message: "Could not retrieve data from the Regular Labs website. Please try again later"

The reason can simply be that you are no longer logged in. In other words, your session has expired.
Try to reload the page and log in to the administrator again.

If you are logged in, then there is something blocking the connection. This can be down to different things. Please check these in order:

  1.  You have a firewall extension getting in the way
    If you have an extension like RS Firewall or AdminTools installed, disable these (temporarily) to see if that is the cause of the issue.
  2. Your host is blocking the connection.
    It can be that your host is blocking the regularlabs.com domain name or IP address. Or it might be blocking remote url calls altogether. Ask your host if they can see why the page is failing.
  3. The regularlabs.com server is blocking the connection.
    It can be that there is some block at the host Regular Labs uses. If the above things don't reveal anything, ask your host to perform a traceroute from your server to the download.regularlabs.com domain/IP. And then pass that along to the Regular Labs support via the forum.

I get the message: "Error connecting to the server: download.regularlabs.com"

See the previous answer.