PHP Loop with Conditional Statement for CURL Execution

I am using 2 functions to execute a CURL. The first function retrieves and store a token while the other executes the order with the token stored.

I am using file_put_contents and file_get_contents to store and retrieve the token.

Function A:

function functionA() {
$ch = curl_init();

$url_token = $this->config['TOKEN'];
$id = $this->config['ID'];
$secret = $this->config['SECRET'];

curl_setopt($ch, CURLOPT_URL, $url_token);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_HEADER, FALSE);

curl_setopt($ch, CURLOPT_POST, TRUE);

curl_setopt($ch, CURLOPT_POSTFIELDS, "{
  \"client_id\": \"$id\",
  \"client_secret\": \"$secret\",
  \"grant_type\": \"client_credentials\"
}");

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
  "Content-Type: application/json",
  "Accept: application/json"
));

$response = curl_exec($ch);
curl_close($ch);

$json = json_decode($response, true);
$file = 'key.txt';
$token = $json['access_token'];

file_put_contents('./modules/custommodule/key.txt', $token, LOCK_EX);

//return $token;
}

Function B:

$file = './modules/custommodule/key.txt';
$retrieved_token = file_get_contents($file);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url_order);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_HEADER, FALSE);
curl_setopt($ch, CURLOPT_POST, TRUE);

curl_setopt($ch, CURLOPT_POSTFIELDS, "{
  \"service_type\": \"xxx\",
  \"service_level\": \"xxx\",
  \"requested_tracking_number\": \"xxx\",
  \"reference\": {
    \"merchant_order_number\": \"xxx\"
  },
  \"from\": {
    \"name\": \"xxx\",
    \"phone_number\": \"xxx\",
    \"email\": \"xxx\",
    \"address\": {
      \"address1\": \"xxx\",
      \"address2\": \"xxx\",
      \"area\": \"xxx\",
      \"city\": \"xxx\",
      \"state\": \"xxx\",
      \"country\": \"xxx\",
      \"postcode\": \"xxx\"
    }
  },
  \"to\": {
    \"name\": \"xxx\",
    \"phone_number\": \"xxx\",
    \"email\": \"xxx\",
    \"address\": {
      \"address1\": \"xxx\",
      \"address2\": \"xxx\",
      \"area\": \"xxx\",
      \"city\": \"xxx\",
      \"state\": \"xxx\",
      \"country\": \"xxx\",
      \"postcode\": \"xxx\"
    }
  },
  \"parcel_job\": {
    \"pickup_instruction\": \"xxx\",
    \"delivery_instruction\": \"xxx\",
    \"delivery_start_date\": \"xxx\",
    \"delivery_timeslot\": {
      \"start_time\": \"xxx\",
      \"end_time\": \"xxx\",
      \"timezone\": \"xxx\"
    },
    \"dimensions\": {
      \"size\": \"xxx\"
    }
  }
}");

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
  "Content-Type: application/json",
  "Accept: application/json",
  "Authorization: Bearer $retrieved_token"
));

$response = curl_exec($ch);
$httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

if ($httpcode === 401) {
    functionA();
    }
}

curl_close($ch);

file_put_contents('./modules/custommodule/response.txt', $response, LOCK_EX);
file_put_contents('./modules/custommodule/results.txt', $httpcode, LOCK_EX);

As you can see, I will need to re-run Function A before initiating Function B if the token has expired. I have used the status 401 that I store as a variable $httpcode.

I am unsure how to re-run Function B upon getting the new/refreshed token. Which loop and condition should I be implementing to achieve this?

Can anyone point this out? Any assistance is greatly appreciated.

Thank you.