There is an issue in the azurerm_policy_set_definition documentation. The optional group_names attribute should be documented as policy_group_names, as is it’s actual name as seen in the tfstate files. I spent quite some time on this trying different things, please update to save others from wasting time discovering this issue azurerm_policy_set_definition | Resources | hashicorp/azurerm | Terraform Registry
tl;dr: group_names attribute should be documented as policy_group_names.
Since this seems to be a bug report, I’d suggest opening a bug report issue in the provider repository, since then it’ll be in the queue for the provider dev team to review and hopefully fix, whereas this forum is more for general discussion and so I can’t be sure that someone on the team will see this and take action based on it.
