Start your own SaaS platform that allows people to use their Android mobile devices as SMS gateways.
Demo: https://codecanyon.net/item/zender-android-mobile-devices-as-sms-gateway-saas-platform/26594230
Whatsapp Gateway | Multi Device (MPWA) is a new build source code and is not an update from the previous MPWA gateway (legacy version), although the layout and appearance is similar to the previous legacy 5 version, but the backend and structure are very different.
Demo: https://m-pedia.co.id/product/whatsapp-gateway-v75-multi-devices