Add custom content to the PMPro login form.

pmpro-login-custom-html-message.php

<?php
/**
 * Add custom HTML at the begining of the PMPro login form.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function my_pmpro_login_custom_html_content( $content ) {

	#--- SETTINGS ---#

	// Enter your custom HTML content/message here:
	$html = '<p class="login-content">Your HTML content here</p>';

	#--- END SETTINGS ---#

	/* That's it, no further editing required */

	// Let's only do this if PMPro is active
	if ( ! defined( 'PMPRO_VERSION' ) ) {
		return $content;
	}

	// Are we on the PMPro login page
	if ( pmpro_getOption( 'login_page_id' ) && is_page( pmpro_getOption( 'login_page_id' ) ) ) {
		// Lets add in our custom HTML at the beginning.
		$content = $html . $content;
	}

	return $content;
}
add_filter( 'login_form_top', 'my_pmpro_login_custom_html_content' );