If an offeree rejects an offer, they can't accept the same offer again later on. If the offer is made to a group, one person's rejection will not stop the rest of the offeree from being able to accept.
Where a buyer is required to give consent through technological means, the contract is made when the buyer has received acknowledgement of receipt from the service provider.
Consideration is 'some right, interest, profit or benefit accruing to one party, or some forbearance, detriment, loss or responsibility given, suffered or undertaken by the other.