Dear Sir,
I have done the same thing last month for one of my client. Because of the APP ID & X-EBAY-API-APP-ID HTTP header are deprecated on July 01st of 2021, they said to use "X-EBAY-API-IAF-TOKEN", I can create this for you to use for Shopping API continuously, I have done in PHP.
Please discuss with me in details, I am looking forward your reply.
Thank you
Regards.