Im sorry for the bad or stupid question but, the back case of my S21 (gifted) is very weak after getting a small part of it was repaired, I concluded that they either used little glue or its a weak type. I currently don't have money on me so I'm worried if this will cost me huge. This is experience from having to pay huge sums for small repairs.
Sometimes secondhand repair shops like in Greenhills provide a kind of adhesive that usually doesn't adhere well especially if you use it right after they put in the adhesive. Since your phone is being used then it will run up the temperature making the adhesive ineffective. I had this issue with my old device (Galaxy A13). My personal advice would be get a durable case for it to protect the back and save up for repairs or you can try to trade-in for a new device, or get a postpaid plan with device. How you proceed is really up to your budget and discretion. I hope this helps 🙏.
