Similarities with a self-employed principal activity

• you must pay per quarter 
• your contribution is a percentage of your revalued reference income
• the contribution percentage is the same
• there is a system for provisional and definite contributions

When your reference income does not exceed a certain amount, you are not obliged to pay contributions.

Your social security
If you exercise an independent secondary activity, you will enjoy the social benefits of the system to which you are subject because of your principal activity (employee, civil servant, pensioner).
The contributions paid by you will contribute to the balance of the system for self-employed persons and, in principle, do not give rise to any rights. 
However, contributions paid on a reference income exceeding the amount on which the minimum contributions for a primary activity are calculated can result in certain rights.

Reimbursement of your contributions in case of a failed start