Hi, as said before, I think we say 'It supposed to happen" in french Ce n'était pas censé se produire or Il est supposé d'arriver" Bonne Chance

"C'est supposé arriver". or "ça devait arriver"

Hello Areej, "It suppose to happen" se dit "c'est supposé arriver" or "c'est supposé être arrivé"... but it depends what's happen... we need the context here to translate and stay close to the meaning.

Try to use google translation site, it works with translation memory

It's supposed to happen... C'est supposé arriver... / C'est censé arriver...