Unfortunately at the time of writing, all of the other answers to this question are incorrect - that is if you're trying to change the price of a hosted button; which is what the question was about.
The correct way to do this is below:
Important Notes: When you update the button details, it isn't just updated for that users session, it updates it within your paypal account - so the new name/price etc will affect all users that attempt to use it.
Also, be advised when altering the contents of a hosted button you need to pass all the details of the button to it as when you created it; so as an example, if you leave out passing it an item name the item name will be blank and Paypal will allow the user to set it.
On that note, we shall continue..
I personally started with this class:
<?php
class Paypal
{
/**
* Last error message(s)
* @var array
*/
protected $_errors = array();
/**
* API Credentials
* Use the correct credentials for the environment in use (Live / Sandbox)
* @var array
*/
protected $_credentials = array(
'USER' => 'seller_1297608781_biz_api1.lionite.com',
'PWD' => '1297608792',
'SIGNATURE' => 'A3g66.FS3NAf4mkHn3BDQdpo6JD.ACcPc4wMrInvUEqO3Uapovity47p',
);
/**
* API endpoint
* Live - https://api-3t.paypal.com/nvp
* Sandbox - https://api-3t.sandbox.paypal.com/nvp
* @var string
*/
protected $_endPoint = 'https://api-3t.sandbox.paypal.com/nvp';
/**
* API Version
* @var string
*/
protected $_version = '74.0';
/**
* Make API request
*
* @param string $method string API method to request
* @param array $params Additional request parameters
* @return array / boolean Response array / boolean false on failure
*/
public function request($method, $params = array())
{
$this->_errors = array();
if (empty($method)) { //Check if API method is not empty
$this->_errors = array('API method is missing');
return false;
}
//Our request parameters
$requestParams = array(
'METHOD' => $method,
'VERSION' => $this->_version
) + $this->_credentials;
//Building our NVP string
$request = http_build_query($requestParams + $params);
//cURL settings
$curlOptions = array(
CURLOPT_URL => $this->_endPoint,
CURLOPT_VERBOSE => 1,
CURLOPT_SSL_VERIFYPEER => true,
CURLOPT_SSL_VERIFYHOST => 2,
CURLOPT_CAINFO => dirname(__FILE__) . '/cacert.pem', //CA cert file
CURLOPT_RETURNTRANSFER => 1,
CURLOPT_POST => 1,
CURLOPT_POSTFIELDS => $request
);
$ch = curl_init();
curl_setopt_array($ch, $curlOptions);
//Sending our request - $response will hold the API response
$response = curl_exec($ch);
//Checking for cURL errors
if (curl_errno($ch)) {
$this->_errors = curl_error($ch);
curl_close($ch);
return false;
//Handle errors
} else {
curl_close($ch);
$responseArray = array();
parse_str($response, $responseArray); // Break the NVP string to an array
return $responseArray;
}
}
}
?>
Credit: https://www.smashingmagazine.com/2011/09/getting-started-with-the-paypal-api/
Then I did the below:
include(dirname(__FILE__) . '/includes/paypal.class.php');
$paypal = new Paypal();
// Set our method
$method = 'BMUpdateButton';
// Set our params
$params = array(
'HOSTEDBUTTONID' => 'your_button_id',
'BUTTONTYPE' => 'BUYNOW',
'BUTTONSUBTYPE' => 'SERVICES',
'L_BUTTONVAR0' => 'item_name=Your Description',
'L_BUTTONVAR1' => 'amount=999.00',
'L_BUTTONVAR2' => 'currency_code=AUD',
'L_BUTTONVAR3' => 'cancel_return=http://www.example.com/cancel.html',
'L_BUTTONVAR4' => 'return=http://www.example.com/success.html'
);
// Make request to change button details
$result = $paypal->request($method, $params);
Note that while Paypal say that BUTTONSUBTYPE is optional, you will likely get an error if you don't include it.
Unfortunately the Paypal docs aren't very clear and don't provide the greatest examples, so I hope this saves someone else the many hours I spent finding out how to do this.
