Whatsapp API Expert needed to advise on PHP web app integration

I have a PHP web application It is mostly Point of Sale (POS) web application which also has a side of Patients Records Management. I need to integrate Whatsapp API in my software whereby i can send, for example, appointment reminders to customers. I already have my PHP developers. You don't need to code in my software. You need to handle the Whatsapp side of things. For example, my PHP dev tried to make me give him access on the Meta Business Account but we are running into error message by Meta. We are not used to this so maybe we are doing something wrong. So i need someone who can assist me in setting up the app on my Meta Account and assist me and my PHP developers in the integration Gradually i want to extend the scope of the whatsapp messages from appointment reminders to sending customers their monthly statement of account, etc. I want someone robust who knows the ins and outs of Meta and Whatsapp.