Why not "il faut..."
"Il faut que tu écrives à Paul" or "Il faut que vous écriviez à Paul" are valid alternatives and both are accepted in translation.
Why is Paul always absent, and why is everyone who works in IT called Dave or Andy?
Vous avez ecrire a Paul" is marked wrong, please explain why?
"To have to" does not translate to "avoir" but to "devoir" or "il faut":