openssl_decrypt(): IV passed is only 12 bytes long, cipher expects an IV of precisely 16 bytes....

[hasanuzzamanbe]

Creating the IV manually needs to be 16 bytes long for algorithms like AES. Where the proper IV is not created throws a critical warning like this:
Warning: openssl_decrypt(): IV passed is only 12 bytes long, cipher expects an IV of precisely 16 bytes, padding with \0 in /var/www/frameme.org/wp-content/plugins/fluent-smtp/app/Functions/helpers.php on line 826

We just have to ensure the 16 bytes iv, we may use padding into it like this:

if (strlen($iv) < 16) {  
    $iv = str_pad($iv, 16, "\0");  // Pad with null bytes if it's shorter  
}