Notice: Undefined index: primary in domain_mapping.php on line 374

Notice: Undefined index: primary in /var/www/html/metro_aux/wp-content/mu-plugins/domain_mapping.php on line 374

Notice: Undefined index: primary in /var/www/html/metro_aux/wp-content/mu-plugins/domain_mapping.php on line 377

sorry running in PHP strict mode 🙂

had a dig into the code and here is patch

--- a/wp-content/mu-plugins/domain_mapping.php
+++ b/wp-content/mu-plugins/domain_mapping.php
@@ -371,10 +371,12 @@ function dm_handle_actions() {
 			case "add":
 				do_action('dm_handle_actions_add', $domain);
 				if( null == $wpdb->get_row( "SELECT blog_id FROM {$wpdb->blogs} WHERE domain = '$domain'" ) && null == $wpdb->get_row( "SELECT blog_id FROM {$wpdb->dmtable} WHERE domain = '$domain'" ) ) {
-					if ( $_POST[ 'primary' ] ) {
+					$primary = 0;
+					if ( array_key_exists( 'primary', $_POST ) ) {
 						$wpdb->query( $wpdb->prepare( "UPDATE {$wpdb->dmtable} SET active = 0 WHERE blog_id = %d", $wpdb->blogid ) );
+						$primary = 1;
 					}
-					$wpdb->query( $wpdb->prepare( "INSERT INTO {$wpdb->dmtable} ( <code>id</code> , <code>blog_id</code> , <code>domain</code> , <code>active</code> ) VALUES ( NULL, %d, %s, %d )", $wpdb->blogid, $domain, $_POST[ 'primary' ] ) );
+					$wpdb->query( $wpdb->prepare( "INSERT INTO {$wpdb->dmtable} ( <code>id</code> , <code>blog_id</code> , <code>domain</code> , <code>active</code> ) VALUES ( NULL, %d, %s, %d )", $wpdb->blogid, $domain, $primary) );
 					wp_redirect( add_query_arg( array( 'updated' => 'add' ), $url ) );
 					exit;
 				} else {

https://wordpress.org/plugins/wordpress-mu-domain-mapping/