diff --git a/lib/MgmtPointMessaging.cs b/lib/MgmtPointMessaging.cs
index 486832f..1b5c0a6 100644
--- a/lib/MgmtPointMessaging.cs
+++ b/lib/MgmtPointMessaging.cs
@@ -572,7 +572,7 @@ public static async void SendPolicyAssignmentRequestWithExplicitData(string mach
             string szMediaGUIDPlain = szMediaGUID.Trim(new char[] { '{', '}' });
             string szMediaGUIDCurlyBrackets = $"{{{szMediaGUIDPlain}}}";
 
-            (MessageCertificateX509 signingCertificate, MessageCertificateX509 encryptioncertificate, SmsClientId _) = GetCertsAndClientId(null, null, szEncodedSigningCert, machineGUID, null, null, null, szMediaGUIDCurlyBrackets.Substring(0, 31));
+            (MessageCertificateX509 signingCertificate, MessageCertificateX509 encryptioncertificate, SmsClientId _) = GetCertsAndClientId(null, null, szEncodedSigningCert, machineGUID, null, null, null, szMediaGUIDCurlyBrackets.Substring(1, 31));
             if (signingCertificate == null)
             {
                 return;
@@ -840,4 +840,4 @@ public static X509Store StoreCertificate(X509Certificate2 certificate, string st
             return x509Store;
         }
     }
-}
\ No newline at end of file
+}