So since theres no tutorials how to make roblox avatars I’ll try to make one and explain it the best I can. Sadly there’s no R15 tutorials how to do it so i would recommend doing R6 avatars.
Things you need:
Unity 2018 4.20
Blender (any version)
VRCHAT SDK 2 (I used to import my roblox avatar into vrchat)
1st step: Would recommend watching this video first bc it got all you need for rigging the avatar for the roblox avatar: https://youtu.be/MzjV5IeFnIg
2nd step: go to blender and add some shoulder bones named “Collar.L and Collar.R”.
3rd step: after all of that you can go to unity and upload your avatar! If it says anything about no shoulders you will need to put the shoulder bones on there yourself by going to configure and go to left arm and right arm and put the collar bones on there.
Hope that was helpful, if you got any problems doing this I’ll make sure to reply to your comment.
Have a nice day!