You should avoid using merged cells (row 4) and that kind of layout. I partially rebuilt your table ( colored background starting DATA sheet A31) to a simple excel list which is much more efficient.You can then add all you want keeping the layout.
From there, a simple XLOOKUP does the trick. (adapt the ranges or make your range an Excel Table,...)

PS ça devrait le faire sans difficultés

Attached Files

Calculateur VenteCommission (Ver.2.0).xlsx (19.8 KB, 5 views)

__________________
Using O365 v2503 - Did you know you can thank someone who helped you? Click on the tiny scale in the right upper hand corner of your helper's post