Two separate flows of money, and one word that covers both.
The option fee is the payment you make once, at the start, to buy the right to purchase the property later at an agreed price. Say $5,000 on a $250,000 house. It's normally non-refundable, meaning if you never buy, the owner keeps it. That's the price of holding the right, and it's separate from whether it gets applied to the purchase. Most contracts do credit it against the price if you do buy, so both things in what you read can sit in the same paragraph without contradiction.
Rent credit is the portion of each monthly payment that gets set aside toward the purchase. If market rent is $1,600 and you pay $1,800 with $200 credited, over 24 months that's $4,800 built up. Add the $5,000 option fee and you'd be bringing $9,800 to the table.
"Option consideration" is the legal umbrella term for whatever you're giving in exchange for the option. In practice it usually means the up-front fee, sometimes fee plus credits. It isn't a fourth payment.
One thing that'll matter more than the labels: the option to purchase should be a separate document from the lease, not a clause buried inside it. Practitioners are firm on that, and how a court treats a combined document varies by state. Ask whoever drafts it why they structured it the way they did, and get the answer in writing.
Also check whether the credit survives a late payment. Plenty of agreements void the whole accumulated credit after one or two late rents.