Require user to confirm there email address before checking out for specific levels.

my_pmpro_require_email_confirmation_for_checkout.php

<?php

/*
 * Require user to confirm there email address before checking out for specific levels.
 * Can build a free level requiring email confirmation for users to sign up for before the "real" 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 my_pmpro_require_email_confirmation_for_checkout( $okay ) {
	$confirmation_levels = array( 1 ); // Email confirmation is required before purchasing one of these memberhsip levels.
	
	global $pmpro_level, $current_user;
	if ( $okay && in_array( intval( $pmpro_level->id ), $confirmation_levels ) ) {
		if ( empty( $current_user->ID ) ) {
			pmpro_setMessage("You must register for the free membership level and confirm your email address before purchasing this memberhsip level.", "pmpro_error");
			$okay = false;
		} else {
			//if they haven't validated yet, don't let them check out
			$validation_key = get_user_meta( $current_user->ID, "pmpro_email_confirmation_key", true );

			if ( $validation_key !== 'validated' ) {
				pmpro_setMessage("You must register for the free membership level and confirm your email address before purchasing this memberhsip level.", "pmpro_error");
				$okay = false;
			}
		}
	}

	return $okay;
}
add_action("pmpro_registration_checks", "my_pmpro_require_email_confirmation_for_checkout");