"I am going to pay you" is it "voy a pagarte" or "voy pagarte"?
Anytime you use a verb that has something to do with motion, place an "a" between the infinitive or the conjugated form of the verb and the infinitive verb that follows.
I'm going to pay you - voy a pagarte
I'm going out to eat - Salgo a comer
I'm coming to see you - Estoy viniendo a verte