An outcome-linked fee is only fair if both sides agree on what the outcome is. Bookings are a promise. Invoiced revenue is a claim. Collected cash is a fact.
That is why fees are calculated on attributable collected revenue: revenue × attribution share × collection rate × fee rate. Attribution share exists because not all India revenue was created by the partner. Collection rate exists because a fee on uncollected invoices punishes the client twice.
For physical products the base changes to contribution margin. Gross revenue can include product cost, duties, freight, marketplace fees, channel margin, discounts, returns and warranty cost. A fee on gross revenue would reward top-line volume even when each unit loses money.
Registered opportunities make this workable in practice. Accounts and partners are registered as they enter the pursuit, so nobody argues about attribution after the cash arrives.