Why are my capsicum (shimla mirch) fruits getting black sunken spots at the bottom?

Black, sunken, leathery spots at the blossom end of capsicum and chilli fruit are blossom end rot, a physiological disorder caused by calcium not reaching the fruit, not a disease. It is triggered mainly by uneven watering, water stress, very high humidity swings or salinity and excess nitrogen, which all block calcium movement even when soil has enough calcium. Fix it by keeping soil moisture steady, ideally with drip and mulch, avoiding both drought and waterlogging, and not over applying nitrogen and potassium. Where soil calcium is low, correct it based on a soil test, and foliar calcium sprays can give temporary relief on affected plants. Remove affected fruits. Maintaining stable moisture is the real solution; confirm any calcium correction with a soil test and your KVK.