Do you have same version you can check in corner it will say like 1.14.30 1.14.60 1.16.0 1.15 like that you can comment any version to me or check if it’s the same if It’s not then that’s the problem you can update but it might take a long time maybe but 1.16.0 is up on mobile and if that’s on your friends phone then you have to update too and then try joining it will work
