According to the documentation, the

group_instance_key

parameter should accept either the unique ID or the URL-friendly key (slug) you specified when creating the group (1) . The API documentation states: "Either the unique id of the resource instance, or the URL-friendly key of the resource instance (i.e: the 'slug') " (1) (2) . Based on your report that only the internally generated IDs work while your custom instance keys don't, this appears to be a bug with the API endpoints. To help our engineers investigate this issue, could you please provide: 1. Which Workspace / Project / Env you are using 2. What calls you are performing (as SDK code or CURL) - specifically showing both the group creation call with your custom

group_instance_key

and the subsequent user assignment call 3. Which PDP version you are running 4. Relevant logs from your PDP In the meantime, as a workaround, you can continue using the internally generated IDs from the List

To learn more, see the sources I considered: [[1] PUT /v2/schema/{proj_id}/{env_id}/groups/{group_instance_key}/users/{user_id}](https://api.permit.io/v2/redoc#tag/Groups/operation/assign_user_to_group) [[2] GET /v2/schema/{proj_id}/{env_id}/groups/{group_instance_key}](https://api.permit.io/v2/redoc#tag/Groups/operation/get_group) [[3] GET /v2/schema/{proj_id}/{env_id}/groups/direct](https://api.permit.io/v2/redoc#tag/Groups/operation/list_direct_group)