Because they’re 2 different requests, and the post doesn’t carry over to the AJAX request from the initial load. Nothing is remembered between page loads, and once the page is generated, nothing persists on the server. It’s a clean slate every time, so why would it remember the post variable?
When you request the page, there’s a post loop and a main query that WP created, and calls the the_post that set up the current post. That’s why it works the first time.
But when you make your AJAX request, there’s none of that, after all how is it supposed to know? Each request is isolated and its own thing. It doesn’t have a URL to pull query variables from and do a query/template, in fact there is no post query in an admin AJAX request unless you do one yourself
So, the AJAX request needs the post ID, but it doesn’t have that information, so send it!
data: {
action: 'getmyfunctionform1',
post_id: <?php echo get_the_ID();?>
},
You can now do $_POST['post_id']
Some further notes
Security
This is insecure:
success: function(response) {
jQuery("#myResultsform1").html(response);
}
Especially if you’re not using SSL, anybody can intercept and insert anything into the page. Instead, it should return data, not HTML, then use the data to build the HTML in JS.
Naming
myfunctionform1 tells us nothing about what this actually does, perhaps a better name would be wccaf_uk_affiliate_link_ajax_handler?
The REST API
WP Admin AJAX is old, and when it doesn’t work it’s painful, a complete black box with no clues.
Why not use the simpler REST API instead?
Register an endpoint, e.g. example.com/wp-json/arabtornado/v1/affiliate_link
add_action( 'rest_api_init', function () {
register_rest_route( 'arabtornado/v1', '/affiliate_link/', array(
'methods' => 'GET',
'callback' => 'arabtornado_generate_link'
) );
} );
Note the callback arabtornado_generate_link, that’s the function that does the work:
function arabtornado_generate_link( $request ) {
$post_id = $request['post_id'];
// etc.. generate response
$result = "https://example.com/affiliate";
return $result;
}
Hey presto:
var url="https://example.com/wp-json/arabtornada/v1/affiliate_link?post_id=1";
jQuery.get( url ).done( function( data ) {
jQuery("#myResultsform1").text( data );
}).fail( function() {
jQuery('#myResultsform1').text("couldn't contact server");
});
If it doesn’t work, it’ll just tell you what the problem was in the response so look at the network panel in your browsers dev tools