You will usually receive a notification informing you about this. However, if you don't receive it, you can check your outstanding debts through this link.
You will be able to view all your debts and obtain the payment document to settle them and regularize your situation.
This debt document is not immediate. It will take a few days to appear. Make sure to check the website in the days following the missed payment, and once it appears, you can pay your outstanding quota through the available methods.
What will happen with the unpaid fee?
Each unpaid quota includes a penalty.
If you are benefiting from the old reduced rate or the current reduced rate, you will have to pay your outstanding quota without that reduction. This means you will pay the full quota for that month along with a surcharge and late payment interest. These interests will increase the longer you go without settling your debt.
Can I deduct this fee?
From the payment of your outstanding fees, you can only add the portion corresponding to the quota as a deductible expense. The late payment interest and the surcharge are not deductible expenses.