redirect_from_post_restricted_to_specific_user_id_or_role.php

<? php
/**
 * Only allow specific users or user roles to view a set of specific posts
 * and redirect users that doesn't meet the set criteria away from the post.
 *
 * 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 redirect_from_post_restricted_to_specific_user_id_or_role() {
	/* SETTINGS */

	// Set your post/page id's here
	$posts_array = array( 2, 35, 156 );  // array elements must be integers and not strings

	// Set the user ID's that has exclusive access to these posts here
	$allowed_user_ids = array( 29, 121, 134 );

	// Set roles here that will receive access to all member content.
	$allowed_user_roles = array( 'editor', 'administrator' );

	// Set URL to which not allowed users should be redirected to.
	$redirect_to_url = home_url();

	/* END SETTINGS - No further editing required */

	// Let's get the user
	global $current_user;

	// get the post ID
	$post_id = get_the_id();

	// Let's check if this if we need to manage this post
	if ( ! in_array( $post_id, $posts_array ) ) {
		return;
	}

	// Let's check if the user should have access to our custom restricted posts.
	if ( in_array( $current_user->ID, $allowed_user_ids ) ) {
		return;
	}

	// This user's ID wasn't included in the allowed users array, let's check if they belong to an allowed role.
	foreach ( $allowed_user_roles as $key => $role ) {
		if ( in_array( $role, (array) $current_user->roles ) ) {
			//Give access if the user has an allowed role
			return;
		}
	}

	// This user didn't meet the restriction criteria, let's redirect them
	wp_redirect( $redirect_to_url );
	exit;
}
add_action( 'template_redirect', 'redirect_from_post_restricted_to_specific_user_id_or_role' );

Post content can also be restricted using the pmpro_has_membership_access_filter hook.
https://gist.github.com/ipokkel/4eb72310157d458363bab993a2a18981