Help give me this error when doing query in Mysql Uncaught Error: Call to undefined function mysql_error ()?

Hello, I do not know why you give me that error, please help is urgent, what I want to do is send a file to the server (if it is sent), but it does not save the files in the Mysql database, the PHP version is 7.3.0 This is my code:

include 'config.php';

if(is_uploaded_file($_FILES['archivo']['tmp_name'])) {
    $ruta = $_SERVER['DOCUMENT_ROOT'].'/subir_archivo/uploads/';
    $nombrefinal= trim ($_FILES['archivo']['name']); //Eliminamos los espacios en blanco
    $nombrefinal= preg_replace ("[^A-Za-z0-9]", "", $nombrefinal);//Sustituye una expresión regular
    $upload= $ruta . $nombrefinal;  

    if(move_uploaded_file($_FILES['archivo']['tmp_name'], $upload)) { //movemos el archivo a su ubicacion 

                echo "<b>Upload exitoso!. Datos:</b><br>";  
                echo "Nombre: <i><a href=\"".$ruta . $nombrefinal."\">".$_FILES['archivo']['name']."</a></i><br>";  
                echo "Tipo MIME: <i>".$_FILES['archivo']['type']."</i><br>";  
                echo "Peso: <i>".$_FILES['archivo']['size']." bytes</i><br>";  
                echo "<br><hr><br>";

               $numCertificado  = $_POST["numeroCertificado"]; 
               $razonSocial  = $_POST["razonSocial"]; 
               //$fecha = $_POST["fecha_expedicion"];
               $direccion = $_POST["direccion"];

               $mysqli -> query = ("INSERT INTO Certificado (numeroCertificado,razonSocial,direccion,ruta) 
                VALUES ('$numCertificado','$razonSocial','$direccion', 
                        '".$numCertificado."',
                        '".$razonSocial."',
                        '".$direccion."')");

    }  

 }

the connection code:

<?php
$host = "localhost";
$dbuser = "root";
$dbpwd = "";
$db = "csc_certificaciones";

$conexion = mysqli_connect($host,$dbuser,$dbpwd,$db);
    if(!$conexion)
        die("Connection failed: " . mysqli_connect_error());
    else
        echo "Connected successfully";
?>

the connection does work because I did another test and if it works and stores it in the database, what can I try?