Hi scott. I am also called scott. You are the 5th person in the world who I know (not including anyone famous) to be called scott.
Anyway... A friend had trouble with this too, but it was her with the android (Galaxy s5) and me with the iphone. I could send her messages but she couldnt send me messages.
The number that she had for my phone, kept adding the area code (or some some numbers) on the front of my number.
I live in new zealand, so my number starts with 022, but later on it was changed (on her phone) to 64022. Try entering his raw number again.
So Can your contact send messages to you?
Also make sure that other people can receive your messages and other people can receive his.
If others can receive your messages, And others can receive his messages, and you have the right number in (double check), then I have 1 more theory.
Go to Settings > Phone > Blocked and make sure he inst blocked 😉