You have to top-up your account when you would like to change to a paid subscription after your free trial period or extend your current paid subscription.

GSMG currently only accepts the crypto currenciees ether (ETH) and binance coin (BNB).

Login to your GMSG account and navigate to "Settings" via the main menu:

Scroll down to "Subscription payments":

If you have never made a deposit before, you have to generate a personal ether deposit address by clicking the button that you find there:

Once an address is generate for you, things look like so:

When sending ETH from Binance, make sure to check the "Ethereum" network option like so:

When sending BNB from Binance, make sure to check the "BEP20" network option like so:

Check also this article for some more warnings and disclaimers.