If you tried to purchase a Channel Revenue Token (CRT) after the offering was sold out, you could still express a commitment to buy though you did not pay for a CRT.
If investment commitments sell out during the offering process, a waitlist is typically created at the discretion of the issuer and funding portal. If you are on the waitlist and other investment commitments are canceled, you may move up the waitlist and receive a confirmation of your investment at closing if space becomes available. Some reasons that space may become available include the possibility that not all investors complete payment, or some cancel, as well as other reasons. You are not billed anything for a Commitment transaction.