Authorisation.php

<?php

require_once 'vendor/autoload.php';

use GuzzleHttp\Client;

$client = new Client();

//Enter Client_id
$client_id = '***************************************';

//Enter Client_secret
$client_secret = '************************************';

//Grant Type
$grant_type = 'client_credentials';

/*
This API is used to get the bearer token. The output of this API contains access_token that will
be used as bearer token for the API that we will be going to call.
*/

//Check for errors while fetching the token
try {
    $response = $client->request('POST', 'https://openapiuat.airtel.africa/auth/oauth2/token', [
        'headers' => [
            'Content-Type' => 'application/json',
        ],
        'json'=> ['client_id' => "$client_id",
            'client_secret'   => "$client_secret",
            'grant_type'      => "$grant_type",
        ],
    ]);

    $body = $response->getBody();
    $token = json_decode($body);
    $access_token = $token->access_token;
}

//Throw Errors Here if any
catch (Exception $e) {
    echo 'Whoops something went wrong: '.$e->getMessage();
}