My climbing butter beans have prolific and healthy looking vines but no blooms; vines have been 'mature' for at least 4 weeks. I use organic fertilizer recommended for vegetables.
Growing Butter Beans
Certified GKH Gardening Expert
You may need to consider adding a bean inoculant to the soil. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/edible/vegetables/beans/growing-butter-beans-in-your-garden.htm