Sir here is the proceduce first you must have atleast more credits than your maximun drone bay. Open a two tabs which are the port tab and the ship factory tab. Build a drone then refresh the port tab it will appear your drones numbers. Sent all the drone to the port and then go back to the ship factory it will appear haft of your credits to the build drone. Wether it is 10b if you have 20b of credits. Build it, it will credits you a 10b of drones if you have a 20 b of credits. I am using my mobile phone which is android. I didn't test it to a pc, laptop,ipad,iphone or etc. I want only to fix this bugs.