The groom cannot attend on the day of the contract. Can he appoint someone else to pronounce the acceptance (qabul)?

In the Shafi'i school, the groom may appoint another man to make the acceptance for him, but it must be arranged through the religious office, not informally. The representative pronounces the acceptance, naming the groom he represents. The marriage approval, the letter of appointment (wakalah) and other documents must be prepared beforehand. The religious office will assess whether your situation allows it and on what conditions. Discuss it with the marriage officer in your state as early as possible. If the groom can attend by postponing the date, that option is usually simpler and raises fewer questions. See a contract by video call.