Name screen with LED’s

Hello colleagues, have the following problem. I got a tip from a comrade how to glue a name tag with LED’s. Now I bought and connected the beautiful LED’s. Each time after about 3 weeks the LED’s break for some reason. This is now the 2nd time. I don’t want to buy new LED’s always after 3 weeks. If someone knows about it and can tell me if I still have any resistances dazwis Here is my short description of the LEDs: They are only connected to 12 volts ! Have you switched in series : + LED – —— + LED – —– + LED – —– + LED – —– + LED – —- + LED – —– + LED – always 6 pieces, since one has such a approx. 2.1 – 2.9 volts. As said always after about 3 weeks of the name tag almost 3/4 of the LED’s falls out. Hugely over a few new tips above all about a small short description or drawing. Greetings Mister07