Show a login/register link at the bottom of any post that uses the membership shortcode or the Require Membership Block.

show-login-register-links-on-member-pages.php

<?php
/**
 * Show a login/register link at the bottom of any post that uses the membership shortcode
 * or the Require Membership Block.
 *
 * Note this doesn't check for specific membership levels.
 *
 * 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 show_login_register_links_on_member_pages( $content ) {
	//bail if PMPro isn't loaded
	if ( ! function_exists( 'pmpro_has_membership_access' ) ) {
		return $content;
	}

	//does this post use the membership shortcode?
	if ( ( has_shortcode( $content, 'membership' ) || has_block( 'pmpro/membership', $content ) ) && ! pmpro_hasMembershipLevel() && pmpro_has_membership_access() ) {
		$pmpro_content_message_pre  = '<div class="pmpro_content_message">';
		$pmpro_content_message_post = '</div>';
		$sr_search                  = array( '!!levels!!', '!!referrer!!', '!!login_url!!', '!!levels_page_url!!' );
		$sr_replace                 = array( '', rawurlencode( site_url( $_SERVER['REQUEST_URI'] ) ), wp_login_url(), pmpro_url( 'levels' ) );
		//get the correct message to show at the bottom
		if ( is_feed() ) {
			$newcontent = apply_filters( 'pmpro_rss_text_filter', stripslashes( pmpro_getOption( 'rsstext' ) ) );
			$content   .= $pmpro_content_message_pre . str_replace( $sr_search, $sr_replace, $newcontent ) . $pmpro_content_message_post;
		} elseif ( is_user_logged_in() ) {
			//not a member
			$newcontent = apply_filters( 'pmpro_non_member_text_filter', stripslashes( pmpro_getOption( 'nonmembertext' ) ) );
			$content   .= $pmpro_content_message_pre . str_replace( $sr_search, $sr_replace, $newcontent ) . $pmpro_content_message_post;
		} else {
			//not logged in!
			$newcontent = apply_filters( 'pmpro_not_logged_in_text_filter', stripslashes( pmpro_getOption( 'notloggedintext' ) ) );
			$content   .= $pmpro_content_message_pre . str_replace( $sr_search, $sr_replace, $newcontent ) . $pmpro_content_message_post;
		}
	}

	return $content;
}
add_filter( 'the_content', 'show_login_register_links_on_member_pages', 5 );