@jeanmichel71
I think I understand..
If you want the admin to receive 10% + a fixed fee for each sale (let’s use a fixed fee of $1 as an example)
Then you’d go to: wp admin > woocommerce > wc vendors > commission
Change the Global Commission Type to: Percentage + fee
Enter 90 in the Commission % field
Enter 1 in the Commission fee field
In this scenario, Admin would receive 10% + $1 of each sale; vendor would receive 90% – $1 (fee taken form the vendor’s commission and given to admin).