我正在学习如何在WordPress中设置API选项，但每次在我的functions.php文件中添加代码时都会出现此错误。
我该如何解决这个问题？
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'my_plugin_menu' not found or invalid function name in /Applications/MAMP/htdocs/wp-test-sites/wp-includes/plugin.php on line 525
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'my_plugin_menu' not found or invalid function name in /Applications/MAMP/htdocs/wp-test-sites/wp-includes/plugin.php on line 525
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'my_plugin_menu' not found or invalid function name in /Applications/MAMP/htdocs/wp-test-sites/wp-includes/plugin.php on line 525