How to support unicode characters in a my mysqli based server [duplicate]

I have been tasked to add full unicode support inside our software.
We use Curl to send request to the server, and I am very new to php.
We want to support this type of email:
沙发模型@gmail.com
I tried to create accounts with that name and it fails for both gmail and outlook. But before dropping the feature i need to be 100% sure only utf-8 emails are allowed worldwide. So i want to support wide strings not just utf-8.

Our test database table look like this:
Database table

Here how an user is registered:

$result = mysqli_query($this->m_conn, "INSERT INTO ".self::TABLE_NAME."(EMAIL, LICENSE_KEYS, COMPUTER_CODES, IPS)  VALUES ('$email', '$license', 'null', 'null')");
if (!$result)
    Logger::ExitWithMessage($email, "DB: unable to insert user. SQL error:". mysqli_error($this->m_conn));

If i try to add a chinese user to our test table:

$robertoEmail = "roberto_沙发模型@hotmail.com";
$robertoLicense = "371C-5BE3-6EF4-9DBC-7F65";
        
$result = mysqli_query($this->m_conn, "INSERT INTO ".self::TABLE_NAME."(EMAIL, LICENSE_KEYS, COMPUTER_CODES, IPS)  VALUES ('$robertoEmail', '$robertoLicense', 'null', 'null')");
if (!$result)
    Logger::ExitWithMessage($robertoEmail, "DB: unable to insert user. SQL error:". mysqli_error($this->m_conn));

When I check the table, I get this “roberto_æ²™å‘模型@hotmail.com” as the email:
wrong table email

The email stored in the database is broken. But something strange i query the table with the roberto user(roberto_沙发模型@hotmail.com) it works:

$robertoEmail = "roberto_沙发模型@hotmail.com";

$query = mysqli_query($this->m_conn, "SELECT * FROM `". self::TABLE_NAME. "` WHERE EMAIL='$robertoEmail'");
if (!$query)
    Logger::ExitWithMessage($email, "DB: Can't select. SQL error:". mysqli_error($this->m_conn));

$user = mysqli_fetch_array($query);
mysqli_free_result($query);
    
if (!$user)
{
    error_log("GetUser failed");
    return;
}

// Everything worked!

Even more strange if i try to manually add roberto to the table:

    INSERT INTO `LICENSES_TABLE`(`EMAIL`, `LICENSE_KEYS`, `COMPUTER_CODES`, `IPS`) VALUES ('roberto_沙发模型@hotmail.com', '371C-5BE3-6EF4-9DBC-7F65', 'null', 'null')

I get this:
I get this

The email is reported as “[email protected]”.

How to properly support unicode emails in a mysqli based server?
Thanks!

While it is not relevant. Here how our C++ application send request to the server

RequestResult NetWork::sendRequest(const bool isPost, const std::string& relativeUri, const std::string& body) const
{
    CURL* handle = curl_easy_init();
    if (!handle)
        return RequestResult();

    /* First set the URL that is about to receive our POST. This URL can
     * just as well be a https:// URL if that is what should receive the
     * data.
     */
    curl_easy_setopt(handle, CURLOPT_URL, ("https://www.mywebsite.com/" + relativeUri).c_str());

    // Skip SSL verification.
    // Not required when server use a certificate signed by a trusted CA.
    // @See: https://stackoverflow.com/questions/56739554/is-https-without-ssl-verification-secure-for-local-application
    {
        /*
         * If you want to connect to a site who isn't using a certificate that is
         * signed by one of the certs in the CA bundle you have, you can skip the
         * verification of the server's certificate. This makes the connection
         * A LOT LESS SECURE.
         *
         * If you have a CA cert for the server stored someplace else than in the
         * default bundle, then the CURLOPT_CAPATH option might come handy for
         * you.
         */
        curl_easy_setopt(handle, CURLOPT_SSL_VERIFYPEER, 0L);

        /*
         * If the site you're connecting to uses a different host name that what
         * they have mentioned in their server certificate's commonName (or
         * subjectAltName) fields, libcurl will refuse to connect. You can skip
         * this check, but this will make the connection less secure.
         */
        curl_easy_setopt(handle, CURLOPT_SSL_VERIFYHOST, 0L);
    }

    // Specify the request type
    curl_easy_setopt(handle, CURLOPT_POST, (int)isPost);

    // Specify the body
    curl_easy_setopt(handle, CURLOPT_POSTFIELDS, body.c_str());

    // Specify the write callbaks
    RequestResult requestResult;
    curl_easy_setopt(handle, CURLOPT_WRITEDATA, &requestResult.res);
    curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, CurlWrite_CallbackFunc_StdString);

    // Perform the request
    const CURLcode res = curl_easy_perform(handle);
        
    // Check result
    if (res == CURLE_OK)
    {
        long http_code = 0;
        curl_easy_getinfo(handle, CURLINFO_RESPONSE_CODE, &http_code);
        requestResult.success = http_code < 400;
    }
    else
    {
        _TRACE(requestResult.res);
    }

    // Cleanup
    curl_easy_cleanup(handle);

    return requestResult;
}

As you can see in the declaration the body is a std::string not a wide string. I dont know how it magically works but if email is (roberto_沙发模型@hotmail.com) then the sendRequest body contains (roberto_æ²™å‘模型@hotmail.com). The request is sent and the server understand that the real email is (roberto_沙发模型@hotmail.com)
request is sent