Ummm hello im laye but i have a solution. theres is a small metal box soldered into the pcb in the left side (where the strap is) so you have to open the jbl, remove the left driver, and then put something to hold the small metal box pushed to the pcb to make contact. I know this us a bad explanation of what is going on but if you want more or want to thank me, please dm me in instagram @zisimopoulos_jr Also here is a video for explaining https://m.youtube.com/watch?feature=yout... The video is with a jbl flip 3 but it works with jbl flip 4 too. Hope ive helped…