This will depend on a couple things. First, are you doing cash-based or accrual-based accounting?
If cash-based, it isn’t appropriate to include these potential earnings at all. Income is recognized only when actually received.
If accrual-based, is this income actually earned? In other words, do you have an irrefutable right to it? Perhaps you do, but perhaps you don’t. For example, if you have to maintain a membership for some period to obtain the payment, it is not yet income, because you have no right to it. But assuming the income is yours and only awaits a payout date, it would be appropriate to enter it, but not into a cash account. You might create an asset account named something like
Accrued affiliate income. Monthly, you could use a journal entry to debit that asset account for the amount earned and credit an income account of your choosing (including, possibly one created for this purpose). When actual payment is received, such as from Google, Receive Money in the appropriate bank account and allocate the transaction to
Accrued affiliate income, which will credit the account and move its balance toward zero. (If the payment received encompasses all accrued affiliate income, it will be zero.)