Generating OAuth 1.0 signatures with PHP core code leads to 'invalid signature' error - any ideas?

Question

I am writing to seek assistance regarding an issue I'm encountering with generating an OAuth 1.0 signature in PHP core code.

To provide some context, I have successfully generated the OAuth 1.0 signature using Postman for a particular API. However, when attempting to implement the same logic in PHP core code, I consistently receive an

invalid signature

error.

I have reviewed my code thoroughly and ensured that all the necessary parameters, such as the consumer key, token, nonce, and timestamp, are included and correctly formatted. Additionally, I have double-checked that the secret keys and the signature generation algorithm are identical to those used in Postman.

Despite these efforts, I am still unable to generate a valid OAuth 1.0 signature. I would greatly appreciate any insights, suggestions, or potential pitfalls that I should be aware of when generating the signature in PHP core code. Additionally, if there are any specific libraries or code examples you recommend for generating OAuth 1.0 signatures in PHP, I would be grateful for your guidance.

$consumer_key = "73f3fcdfe03d1c584b4b0698b5860d0c5b06ca5ef18a0b123456b4283b32eba4";
$access_token = "af16e2b3db4fde9bfbd9156ee4bbca3a9874c6c2526d8d244de5ac5ba9c6a187";
$consumer_secret = "df7610c290779e2db7b712d694ff3214a9c895fa7020ba2cc7a8d714eb100635";
$token_secret = "4a34f43d961b39c03d6160a0d8600f3d0e495f963852741c8221d5c2f2939c41";
$realm = "3302600";
$http_method = 'GET';
$url = "https://www.testanywebsite.com/api"; // as we want to generate signature this will be anything
$nonce = mt_rand();
$timestamp = time();

$params = array(
  'oauth_consumer_key' => $consumer_key,
  'oauth_token' => $access_token,
  'oauth_timestamp' => $timestamp,
  'oauth_nonce' => $nonce,
  'oauth_signature_method' => 'HMAC-SHA256',
  'oauth_version' => '1.0'
);

$oauth_signature = generate_oauth_signature($http_method, $url, $params, $consumer_secret, $token_secret);
function generate_oauth_signature($http_method, $base_url, $params, $consumer_secret, $token_secret = '') 
{
  // Percent encode the parameters and sort them alphabetically by key
  $encoded_params = array();
  foreach ($params as $key => $value) {
    $encoded_params[rawurlencode($key)] = rawurlencode($value);
  }
  asort($encoded_params);

  // Concatenate the encoded parameter keys and values with = and & characters
  $param_string = '';
  foreach ($encoded_params as $key => $value) {
    $param_string .= $key . '=' . $value . '&';
  }
  $param_string = rtrim($param_string, '&');

  // Percent encode the base URL and concatenate the HTTP method, encoded base URL, and encoded parameter string with & characters
  $encoded_base_url = rawurlencode($base_url);
  $signature_base_string = $http_method . '&' . $encoded_base_url . '&' . rawurlencode($param_string);

  // Concatenate the consumer secret and token secret (if present) with & characters and use as the HMAC-SHA256 key to generate the signature
  $key = rawurlencode($consumer_secret) . '&' . rawurlencode($token_secret);
  $signature = base64_encode(hash_hmac('sha256', $signature_base_string, $key, true));

  return $signature;
}

using same nonce, timestamp & other credentials generate_oauth_signature function returns signature ---> iUoJTlNUZpGAoBSLkf9gJZExGq9W4E0CXIsKbanpiWY=

while in POSTMAN it returns --->

SUy3g1XdK2wK2TVIieoENK/UAQEFkgpF+ztT7F0aqfc=

I am using the above-shown function to generate the signature, the signature returned from this function is different from POSTMAN. What needs to be changed to generate the same signature as POSTMAN generates?