Reasonable. According to the provisions of this convention, the condition of effective acceptance is that acceptance must agree to the terms of the offer, or conditional acceptance without substantially changing the terms of the offer. In this case, the telex we accepted contains the words "subject to the signing of the confirmation", which is conditional acceptance. Later, because there were some issues to be discussed and the confirmation letter was not signed, it did not constitute effective acceptance, that is, the contract was not established, and the other party asked us to open a letter of credit, and we had the right to refuse.