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Your LimeSurvey version:5.3.5
Own server or LimeSurvey hosting:localhost
Survey theme/template:fruity
==================
When sending an invitation email, there was an error of 500 indicating Invalid MAC. May I ask how to solve it?SodiumExceptionInvalid MACC:\phpstudy_pro\WWW\cp\third_party\paragonie\sodium_compat\src\Crypto.php(1058)1046 );
1047 $verified = ParagonIE_Sodium_Core_Poly1305::onetimeauth_verify(
1048 $mac,
1049 $c,
1050 ParagonIE_Sodium_Core_Util::substr($block0, 0, 32)
1051 );
1052 if (!$verified) {
1053 try {
1054 ParagonIE_Sodium_Compat::memzero($subkey);
1055 } catch (SodiumException $ex) {
1056 $subkey = null;
1057 }
1058 throw new SodiumException('Invalid MAC');
1059 }
1060
1061 /** @var string $m - Decrypted message */
1062 $m = ParagonIE_Sodium_Core_Util::xorStrings(
1063 ParagonIE_Sodium_Core_Util::substr($block0, self::secretbox_xsalsa20poly1305_ZEROBYTES),
1064 ParagonIE_Sodium_Core_Util::substr($c, 0, self::secretbox_xsalsa20poly1305_ZEROBYTES)
1065 );
1066 if ($clen > self::secretbox_xsalsa20poly1305_ZEROBYTES) {
1067 // We had more than 1 block, so let's continue to decrypt the rest.
1068 $m .= ParagonIE_Sodium_Core_Salsa20::salsa20_xor_ic(
1069 ParagonIE_Sodium_Core_Util::substr(
1070 $c,



Stack Trace#0+
  C:\phpstudy_pro\WWW\cp\third_party\paragonie\sodium_compat\src\Compat.php(2343): ParagonIE_Sodium_Crypto::secretbox_open()#1+
  C:\phpstudy_pro\WWW\cp\application\core\LSSodium.php(139): ParagonIE_Sodium_Compat::crypto_secretbox_open()#2+
  C:\phpstudy_pro\WWW\cp\application\models\LSActiveRecord.php(384): LSSodium->decrypt("Gghs1e6uWCMBsbs3waQDmZCylLlym9HlJ7EvfrEAXyA=")#3+
  C:\phpstudy_pro\WWW\cp\application\core\LimeMailer.php(131): LSActiveRecord::decryptSingle("Gghs1e6uWCMBsbs3waQDmZCylLlym9HlJ7EvfrEAXyA=")#4+
  C:\phpstudy_pro\WWW\cp\application\core\LimeMailer.php(230): LimeMailer->__construct()#5+
  C:\phpstudy_pro\WWW\cp\application\controllers\admin\Tokens.php(1397): LimeMailer::getInstance(2)#6 unknown(0): Tokens->email(921475)#7+
  C:\phpstudy_pro\WWW\cp\framework\web\actions\CAction.php(115): ReflectionMethod->invokeArgs(Tokens, array("921475"))

You didn't provide any infos about the hosting environment. Localhost? To stuff you posted indicates a Windows OS.

The cryptoextension is triggering an error which,
The crpytoextension is used because the password in the mailserver credentials are stored encrypted.

I recommend to update LimeSurvey 5 (you use an old version) and check what exact PHP version you currently use and if the PHP extension libsodium is uptodate and enabled. Perhaps you need to update your windows webserver environment.

Maybe try to set again the password too ?