Under the common law, an acceptance cannot deviate from the terms of the offer without being considered either a rejection or a counteroffer. Under UCC Article $2$:

an acceptance is not valid if the offeree's acceptance contains different terms from those in the offer.

an acceptance is valid when the parties intend to form a contract, even if the offeree's acceptance contains different terms from those in the offer.

an acceptance is only valid if it occurs in writing.

an acceptance is only valid if it is communicated orally.