Question

invite a friend come in birthday

Answer 1

Yours name,date etc.... ( letter writing)

Then

Subject:inviting friend for birthday party.

Dear friend,
I hope that you are enjoying your good health. I am fine too. I want to remaind you that my birthday going to be held on 20th separated. Many of my friends are coming on this occasion. So I wish your presence also. I have Some plans ro celebrate my birthday with my friends. When you come I will tell you my plans
I am eagerly waiting for your arrival. Tell my regards to aunt and uncle.

Yours friendly,
Urs name

I hope my answer will help you a lot