diff --git a/stackit/internal/resources/mongodb-flex/instance/resource_test.go b/stackit/internal/resources/mongodb-flex/instance/resource_test.go
index 2c293e4a..fa82be7b 100644
--- a/stackit/internal/resources/mongodb-flex/instance/resource_test.go
+++ b/stackit/internal/resources/mongodb-flex/instance/resource_test.go
@@ -88,6 +88,7 @@ func config(name string) string {
 		name         = "%s"
 		project_id   = "%s"
 		machine_type = "%s"
+		acl = ["193.148.160.0/19","45.129.40.1/21"]
 	}  
 	  `,
 		name,
diff --git a/stackit/internal/resources/mongodb-flex/instance/schema.go b/stackit/internal/resources/mongodb-flex/instance/schema.go
index 99b0a1bf..9a191a84 100644
--- a/stackit/internal/resources/mongodb-flex/instance/schema.go
+++ b/stackit/internal/resources/mongodb-flex/instance/schema.go
@@ -138,7 +138,7 @@ func (r *Resource) Schema(ctx context.Context, req resource.SchemaRequest, resp
 			"acl": schema.ListAttribute{
 				Description: "Access Control rules to whitelist IP addresses",
 				ElementType: types.StringType,
-				Optional:    true,
+				Required:    true,
 				Computed:    true,
 			},
 			"timeouts": common.Timeouts(ctx, timeouts.Opts{