If you have an unpaid invoice, you will see a warning message: Account is on hold displayed on your screen when attempting to access your subscription, as per the photo illustration below.
The message prompts you to pay in order to have continued access to the content you signed up to watch.
To make payment, enter your card details then click Unlock my account.
If you wish to cancel your subscription, change the URL from /on_hold to /dashboard.
Doing so will take you to the dashboard where you can cancel your subscription.
Sample photo illustration
If you wish to sign out of your account instead, simply change the URL from /on_hold to /sign_out.