Keep the money that is not yours somewhere else

A large share of what lands in your account is already committed. Treating the balance as profit is the most common way to end up short.
Separate it on arrival:
— Tax. Set the portion aside the day the money arrives, in a different account. Every business that gets caught out did it by treating a tax liability as working capital.
— Supplier obligations for spend already committed.
— A reversal reserve sized on your own history with that partner.
— Currency exposure. If you earn in one currency and spend in another, the rate moves between the period closing and the money landing. On thin margins that swing is your margin. Decide deliberately whether you are carrying that risk.
— Payment fees on both sides, including conversion spreads that never appear as a line item.
What is left after all of that is the number you are allowed to think of as yours.
The account balance is not the score.