How do I create a subgroup?

I also tried going to /group/ID/subgroup/add/GROUPTYPE but this shows as not existing.

Also note that I've got the site-wide 'developer' role, which has been set as the site admin role (all permissions), and on the parent group permission page, this role has all permissions for the subgroup.

I figured it out. For reference for anyone else who may come across this, the button to create a subgroup is part of the Group Operations block. This block must be placed in a region in the theme. Make sure to check the 'Group ID from the URL' checkbox in the block config. Once this block has been placed, a subgroup can be created from the link in this block.

Automatically closed - issue fixed for 2 weeks with no activity.

In my case i have the same issue where i need subgroup and i haven't found any subgroup tab after installing group module so i found the module from https://www.drupal.org/project/subgroup → , after installing subgroup module i found a tab of it inside the group module.