How to Handle WordPress Errors with WP_Error Class | http://www.ibenic.com/how-to-handle-wordpress-errors-with-wp_error-class

class.php

<?php

$error_code = 'my_error_code';
$error_message = __( 'My Error Message', 'my_textdomain' );

$api_error = new WP_Error( $error_code, $error_message );

paypal.php

<?php

$response_from_paypal = paypal_retrieve_approaval_link();
// We have an error
if( $response_from_paypal['ACK'] != 'SUCCESS' ) {
  $error_code = $response_from_paypal['L_ERRORCODE0'];
  $error_short_message = $response_from_paypal['L_SHORTMESSAGE0'];
  $error_long_message = $response_from_paypal['L_LONGMESSAGE0'];

  $api_error = new WP_Error( $error_code, $error_short_message ); // We have added a short message, it will be the first code
  
  // Let's add a long message with description
  $api_error->add( $error_code, $error_long_message );
}

paypal_get.php

<?php

// ...

$retrieved_error_from_plugin = did_paypal_pay();

// It is a WordPress Error
if( is_wp_error( $retrieved_error_from_plugin ) ) {
  $retrieved_error_from_plugin->get_error_codes();
  /*
   array(
    '10002'
   );
   */
  
  $retrieved_error_from_plugin->get_error_code(); 
  /*
   '10002'
   */
  
  $retrieved_error_from_plugin->get_error_messages( '10002' );
  $retrieved_error_from_plugin->get_error_message( '10002' );
  /* Same:
  array(
    'Authentication/Authorization Failed',
    'Account is locked or inactive'
   );
   */
  
  
  
  $retrieved_error_from_plugin->get_error_messages( '10005' );
  /*
  array() // Empty 
  */
}