Unable to add my phone number to my apple id for people to contact me

I recently updated my phone one day ago, to the new iOS 15.3 software update. After doing this, I received a message from my friend stating that she is unable to message me through iMessage. I found it strange and proceeded to figure why this was happening. I then realized my phone number was not connected with iMessage and the only option I had was to sign in using my apple ID/email. I tried adding my phone number to my apple ID and though it is a valid number, I kept being that it was invalid. I’m asking that someone please help with this because my phone number is literally how individuals contact me through iMessage.