Poor watering. If the plant isn't getting enough water, it causes a disorder in the cells in the fruits through shortage of calcium, which the plant can't take up because its too dry. Improve your watering regime - remove any fruits which have brown ends.

If in containers, and you have very soft water, you may want to apply some limestone or gypsum to provide more calcium. Even adequate calcium won't make up for scanty watering, though.

Thanks to the comments the watering has been scant
Graham

Only a few peppers can stand much drought, and they are all little ones.