English Runner Beans
Why do the flowers drop before the pods are set?
Certified GKH Gardening Expert
General purpose fertilizers contain nitrogen. This will prevent fruit from properly forming on the plants.
Beans are legumes. These types of plants "make" their own nitrogen, and fix it into the soil. Adding any more than that and they will fail to fruit. The best I could suggest, would be to flush out the soil, and be sure that the water can drain extremely well through the pot. Flush it passed the point you would feel is enough.
The only fertilizers you will need will be a specific formula for flowering plants. These will contain phosphorus and potassium, but not nitrogen.
This article will help: https://www.gardeningknowhow.com/edible/vegetables/beans/bean-blossoms-no-pods.htm