Hi Allyson,
My first advice is always “patience” – because breeding birds takes a lot of patience on your end. As you have found, you can have everything set up correctly and still have nothing to show for it. It is important that they are on a nutritionally balanced diet and not just a loose seed mix. They need extra nutrition when breeding, so in addition to a fortified diet, you should offer chopped fruits and veggies, dark leafy greens, cooked eggs and multi grain bread. The nest box should be affixed to the outside of the cage, as high as possible. It is best to wait until the pair shows signs of bonding like preening and feeding each other, as well as mating. Not all pairs will get along or be good breeders. You mentioned the male used to have a mate – did she die? He may not be ready to bond with another female. If she is much younger than him, he may not be interested or she might be too immature for him. All you can do is wait and see if they end up bonding. This can take weeks, months or longer. There is nothing you can do to force them to breed – you just have to wait and hope for the best.
Thank you for asking Lafeber,
Brenda