Calling a function of a class does not work php - php

Question

I have a php file called "purchases.controller.php" in which within a function called 'ctrCash' of the 'Purchases' class, I pass variables to a function called 'ctrNewCashPurchase' of the 'CartController' class that I have defined, but when I run the project, I get the message:
"Fatal error : Uncaught Error: Class 'CartModel' not found in ... "
If I do a var_dump inside the function ctrNewCashPurchase, I realize that I am entering that function, but it tells me that it does not recognize 'CartModel' and I do not understand why.
I share the code of the "purchases.controller.php" file:
class CartController{
static public function ctrNewCashPurchase($datos){
$tabla = "compras";
$respuesta = CartModel::mdlNewCashPurchase($tabla, $datos);
if($respuesta == "ok"){
$tabla = "comentarios";
ModeloUsuarios::mdlIngresoComentarios($tabla, $datos);
}
return $respuesta;
}
}
class Purchases {
public function ctrCash (&$arrayCompleto, &$usuario, &$direccion1, &$direccion2, &$dia, &$hora, &$email, &$telefono, &$sesion){
if(isset($usuario)){
//Here I create an array
for($i = 0; $i < count($arrayCompleto); $i++){
$datos = array("idUsuario"=> $sesion,
"idProducto"=> $arrayCompleto[$i]["idProducto"],
"metodo"=> "Efectivo",
"email"=> $email,
"direccion"=> $direccion1,
"detalleDireccion"=> $direccion2,
"diaEnvio"=> $dia,
"horaEnvio"=> $hora,
"telefono"=> $telefono,
"pais"=> "ARG");
}
$respuesta = CartController::ctrNewCashPurchase($datos);
}
}
}
I share the code of the "purchases.model.php" file, where I define the CartModel class:
class CartModel{
static public function mdlNewCashPurchase($tabla, $datos){
$stmt = Conexion::conectar()->prepare("INSERT INTO $tabla (id_usuario, id_producto, metodo, email, direccion, pais, detalleDireccion, diaEnvio, horaEnvio, telefono) VALUES (:id_usuario, :id_producto, :metodo, :email, :direccion, :pais, :detalleDireccion, :diaEnvio, :horaEnvio, :telefono)");
$stmt->bindParam(":id_usuario", $datos["idUsuario"], PDO::PARAM_INT);
$stmt->bindParam(":id_producto", $datos["idProducto"], PDO::PARAM_INT);
$stmt->bindParam(":metodo", $datos["metodo"], PDO::PARAM_STR);
$stmt->bindParam(":email", $datos["email"], PDO::PARAM_STR);
$stmt->bindParam(":direccion", $datos["direccion"], PDO::PARAM_STR);
$stmt->bindParam(":pais", $datos["pais"], PDO::PARAM_STR);
$stmt->bindParam(":detalleDireccion", $datos["detalleDireccion"], PDO::PARAM_STR);
$stmt->bindParam(":diaEnvio", $datos["diaEnvio"], PDO::PARAM_STR);
$stmt->bindParam(":horaEnvio", $datos["horaEnvio"], PDO::PARAM_STR);
$stmt->bindParam(":telefono", $datos["telefono"], PDO::PARAM_INT);
if($stmt->execute()){
return "ok";
}else{
return "error";
}
$stmt->close();
$tmt =null;
}
}
And I add this other file called 'aux.php' in case it influences something in the error that causes me. Here is how to send 'purchases.controller.php' parameters within the 'ctrCash' function
if(isset($_POST['usuario'])){
require ('purchases.controller.php');
$arrayCompleto = json_decode($_POST['arrayCompleto'], true);
$usuario = $_POST['usuario'];
$direccion1 = $_POST['direccion1'];
$direccion2 = $_POST['direccion2'];
$dia = $_POST['dia'];
$hora = $_POST['hora'];
$email = $_POST['email'];
$telefono = $_POST['telefono'];
$sesion = $_POST['sesion'];
$payments = new Purchases();
$payments -> ctrCash($arrayCompleto, $usuario, $direccion1, $direccion2, $dia, $hora, $email, $telefono, $sesion);
}