Under normal circumstances, Fergus will charge the subscription fee to your card automatically on the first of each month.
However, if something has gone wrong and the transaction is unsuccessful, you will get a banner at the top of the home page to let you know:
If you do see this, don't panic! In most cases the transaction will have not gone through due to problems with your credit card and you have until your next bill is issued to get a replacement.
You can also recharge an outstanding bill to your card in ⚙ Settings > Billing, by way of the "Charge Now" button in the unpaid invoices area.
What happens if my invoice still remains unpaid by the first of the next month?
Fergus will try to recharge the outstanding bill at the same time as the new one - if this is successful then you don't need to worry and can continue as usual.
If this is unsuccessful again however, then you will need to update your credit card information and recharge the invoice to get back into the site.