try-amp-cta.php

<?php
/**
 * Plugin Name: Try AMP CTA
 */

add_filter(
	'the_content',
	function ( $content ) {
		if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
			$content = '<p>CTA!</p>' . $content;
		}
		return $content;
	},
	1000
);

add_action(
	'wp_footer',
	function() {
		if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
			?>
			<amp-user-notification
				layout="nodisplay"
				id="amp-user-notification1"
				data-dismiss-href="https://foo.com/api/dismissed">
				This site uses cookies to personalize content.
				<a href="">Learn more.</a>
				<button on="tap:amp-user-notification1.dismiss">I accept</button>
			</amp-user-notification>
			<?php
		}
	}
);