Hello @Ali Avais
Unfortunately it is not possible to access App Service through IP Address.
App Service is sharing infrastructure with other App Services being deployed in that same region, so there are effectively multiple apps sharing a pool of IP addresses.
When a request comes in to an IP address with no hostname, the system will not know where to route it.
I assume you are going to send SMS from your App Service and you need to know outbound IP addresses.
You can get them in App Service settings