There is already an Apple business api that allows validated businesses to talk to you over iMessage. It does require you to agree not to spam though (try Home Depot on iMessage to see)
hold on someone was distributing stuff at work was told by HR to stop doing it and then kept putting up flyers and using work resources for political stuff and got fired?
The official api for iMessage is far richer than this and has things like forms, quick replies, various pickers, apps you can send in addition to text and images
Right gray bubbles and validated businesses for commercial and blue for people. Apple business chat is not inbound only. 100% of your features including the ability to redirect voice calls to iMessage are already offered by Apple via an api and its integrated into every major crm
how is it possible to build this whole thing and not know there is a very rich first party api that does the same thing and more in iMessage
https://www.apple.com/ios/business-chat/