Update a table when an specific column of another table is updated using trigger in SQL Server

I am using this trigger:

create trigger UpdateCustomerOnWholeSellerIdChange
on Invoice after update
as
begin
    set nocount on;
    if update(WholeSellerId)
    begin
        update Customer
        set Customer.WholeSellerId = d.WholeSellerId
        from deleted d
        where d.CustomerId = Customer.CustomerId
    end
end

What I am trying to accomplish is: each CustomerId has his own WholeSellerId meaning each Customer has their own salesman. In the Invoice table, each Invoice has its own CustomerId and WholeSellerId.

So when I update the WholeSellerId in the Invoice table, I would like to update the WholeSellerId of the Customer table as well to the WholeSellerId of the Invoice table.

With my code above, even when I update my WholeSellerId in the Invoice table, it doesn't update the Customer's WholeSellerId.

Your help is appreciated.