Wordpress update_post_meta does not update dynamic values

Question

This is a little strange, I am using "update_post_meta" to update the custom fields in Wordpress. When I run update_post_meta($post_id, 'Test_Field', 'Test Value'); the custom field updates without a problem BUT when I use a string value it does not update:

$test_value = "Test";
 echo $test_value; // No problem here
 echo $post_id; // No problem here
 update_post_meta($post_id, 'Test_Field', $test_value);

Thanks very much in advance for your help

Stu

Answer 1

Try to cast variables with types. Try this:

update_post_meta( (int) $post_id, 'Test_Field', (string) $test_value );

Answer 2

Your first example used $post_id and solution $page_id. Was that a typo?

Answer 3

It might sound strange but, meta_key name must be identical to the input field name.

update_post_meta( $post_id, 'top_image', $_POST['top_image'] );