Payment agreement problem

Hello everyone, i'm french and i'm looking to get payed but i have a problem with the payment agreement.

I entered the 15 number in my social security number ( carte vital) but this is refused and they say this does not match my information.

I alredy contacted the support, they told me this is a 11 digits format and i found topic saying CGTrader require a 13 digits formats so i'm lost.

Any french that can help me on what is the identification number for us ?

Thanks !