diff --git a/Plugin/unraid/api/flag_toggle.php b/Plugin/unraid/api/flag_toggle.php
index 795265d..77d2067 100644
--- a/Plugin/unraid/api/flag_toggle.php
+++ b/Plugin/unraid/api/flag_toggle.php
@@ -34,10 +34,14 @@
 // OPERATIONAL SAFEGUARDS
 //   POST only, checked before any parameter is read.
 //
-//   The flag name is constrained to the rsync namespace.
-//       ^[A-Z_]+_RSYNC_ENABLED$ — this endpoint cannot be used to flip an unrelated boolean
-//       in master.conf. Every other conf edit goes through confform.php or config.php, which
-//       have their own rules; a general-purpose flag setter would bypass all of them.
+//   The flag name is constrained to the rsync namespace, with the tier prefix optional.
+//       ^([A-Z][A-Z_]*_)?RSYNC_ENABLED$ — this endpoint cannot be used to flip an unrelated
+//       boolean in master.conf. Every other conf edit goes through confform.php or config.php,
+//       which have their own rules; a general-purpose flag setter would bypass all of them.
+//
+//       The prefix must be optional because RSYNC_ENABLED is itself the global gate, and the
+//       page renders it alongside the tier flags. Requiring a prefix rejected it as an invalid
+//       flag name, so the master switch could not be turned on from the UI at all.
 //
 //   Anything other than the literal "1" is treated as false.
 //       ($_POST['enabled'] ?? '0') === '1' — strict comparison against one value, so a
@@ -79,7 +83,11 @@ if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
 $name    = trim($_POST['name']    ?? '');
 $enabled = ($_POST['enabled'] ?? '0') === '1';
 
-if (!$name || !preg_match('/^[A-Z_]+_RSYNC_ENABLED$/', $name)) {
+// The tier prefix is optional. RSYNC_ENABLED itself is the global gate the page also renders,
+// and requiring a prefix silently rejected it — the toggle reverted to off with no way to turn
+// syncing on from the UI at all. Masked until now because every POST to this endpoint was
+// being swallowed by the multipart bug.
+if (!$name || !preg_match('/^([A-Z][A-Z_]*_)?RSYNC_ENABLED$/', $name)) {
     echo json_encode(['ok' => false, 'error' => 'Invalid flag name']);
     exit;
 }