Hi K.Rossarin,
For the authorized person, normally the project owner shall propose the authorized signatory name who will sign the agreement and all supporting docs for each project. So, in this case, please provide the name of authorized signatory to K.Supamit so that he can further prepare a power of attorney. After that, such authorized person can sign supporting documents to be submitted to Alipay/Alitrip ka.
Best regards,
Ying