Your code works well when put in a page template, so what is currently wrong in your case most probably is the usage of the wrong hook in the wrong place.
Just an example of how you can hook this:
add_action('ahook', 'add_page_content_Send_Feed'); //add this after your function definition
Then you can use this in any page or other template of the theme (or other plugin):
do_action('ahook');
‘ahook’ can be a hook you made up, but you can replace it by some specific one that you want to use depending on your specific case.
Another thing you can do is define a shortcode and apply this button just anywhere in your content.