First things first do you have a nesting box? Birds usually will not mate without a nest box as this is where they can built their nest and lay the eggs. It also may not be breeding season. Birds don't breed in colder wether (even if they are indoor).

My female budgie has a brown cere and my male budgie has a darkish blue cere but he won't mate the female he just sings along and bobs up and down why won't he mate the female