Possible Unhandled Promise Rejection (id: 0): Syntaxerror: JSON Parse error: Unrecognized token '<'

Question

I’m developing an app and I need to log in. I have an API on two different servers.

a return me:

Possible Unhandled Promise Rejection (id: 0):  SyntaxError: JSON Parse error: Unrecognized token '<'

and the other:

Possible Unhandled Promise Rejection (id: 0):
SyntaxError: JSON Parse error: Unexpected EOF

Login screen:

const handleSignClick = async () => {
        if(cpfField != '' && passworldField != ''){

            let json = await Api.signIn(cpfField, passworldField);

            if(json){
                alert("DEU CERTO");
            } else {
                alert("CPF e/ou senha errados!");
            }

        } else {
            alert("Preencha os campos!");
        }
    }

Calling for:

signIn: async (cpf, pass) => {

        const req = await fetch(`${BASE_API}/login/index.php`, {
            method: 'POST',
            headers:{
                'Accept': 'application/json',
                'Content-Type':'application/json'
            },
            body: JSON.stringify({cpf, pass})
        });
        const json = await req.json();

        console.log("CPF: ", cpf);
        console.log("Pass: ", pass);
        console.log("Json: ", json);
        return json;
    }

API:

<?php
header("Access-Control-Allow-Origin: *");
header("Access-Control-Allow-Methods: POST, PUT, DELETE, OPTIONS");
header("Content-Type: application/json");  

include 'conexao.php';


$method = strtolower($_SERVER['REQUEST_METHOD']);

if($method === 'post') {
    $array = array('error' =>'');
    
    $data = json_decode(file_get_contents('php://input'));
    if(is_null($data)){
        $data = $_POST;
    }
    
    $cpf = $data["cpf"];
    $pass = $data["pass"];

   // Verifico os dados e retorno 

    header("Content-Type: application/json");
echo json_encode($array);