Unable to Send Messages w/ Phone Number

My iMessage was working fine until one of my friend asked me if I had changed my number, which I obviously didn’t.

I went into my iMessage settings and noticed that there was no checkmark next to my phone number in the “Send & Receive.” My friend told me that the way they had messaged me was by my iCloud email, and that when they tried messaging me by my phone number, they were unable to send the message.

Although my number isn’t grayed out, it would not let me select it for “Send & Receive.” When I click it, a loading mark appears next to it, but then does not select my number as an option.

I have tried looking up this problem online, but I’ve found nothing about it. Even though I can send messages from my emails, it bothers me that I am unable to use my phone number to as a way of sending messages.

Is there a problem that I am unaware of? I would appreciate any replies to my problem.

Thank you.