Hi @alid
There’s one of two ways you could do this.
Method 1
If you like a record of each payment (i.e. who it’s from, what it’s for etc), you could create a new client called ‘Affiliate Income’ (or similar), and raise a new invoice for payment, and tag it as normal.
The invoice itself can be assigned to 4902 Commissions Received.
Method 2
You could tag it straight to the nominal:
Hope that helps!