resource "azurerm_frontdoor_firewall_policy" "example" {

                                            ...
                      policy_settings {
 +                      enabled                     = true
 +                      mode                        = "Prevention"
                        request_body_check          = true
                        file_upload_limit_in_mb     = 100
                        max_request_body_size_in_kb = 128
                      }
                      ...
                    }