try spraying overhead in a morning when the plants are in shade-- it works with tomatoes and cucumbers if they struggle to set

It's a pollination problem, as the female flowers (with the embryo fruit attached at the flower base) won't set otherwise. The male flowers which have no fruit attached fall off anyway. You can try hand pollination by taking a male flower, removing the petals, and rubbing the stamens inside a female flower when it is fully open. The insects should do this for you though, so encourage hover flies, bumble bees, and any other insects in your garden by planting lots of nectar bearing bee plants.

Thanks.sounds a bit complicated!