Only allow users to use the trial levels once with Paid Memberships Pro.

my_pmpro_after_change_membership_level.php

<?php
/**
 * Only allow users to use the trial level once. This does not affect pre-existing members that had a level before this code is implemented.
 * Be sure to change the $trial_levels variable in multiple places.
 * You may add this code to your site by following this guide - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
//record when users gain the trial level
function my_pmpro_after_change_membership_level($level_id, $user_id)
{
	//set this to the id of your trial level
	$trial_levels = array( 1, 2 );
		
	if ( in_array( $level_id, $trial_levels ) ) {	
		//add user meta to record the fact that this user has had this level before
		update_user_meta($user_id, "pmpro_trial_level_used_{$level_id}", "1");
	}	
}
add_action("pmpro_after_change_membership_level", "my_pmpro_after_change_membership_level", 10, 2);
//check at checkout if the user has used the trial level already
function my_pmpro_registration_checks($value)
{
	global $current_user;
	
	$level_id = intval( $_REQUEST['level'] );

	if ( $current_user->ID ) {
		//check if the current user has already used the trial level
		$already = get_user_meta($current_user->ID, "pmpro_trial_level_used_{$level_id}", true);
		
		//yup, don't let them checkout
		if( $already ) {
			global $pmpro_msg, $pmpro_msgt;
			$pmpro_msg = "You have already used up your trial membership. Please select a full membership to checkout.";
			$pmpro_msgt = "pmpro_error";
			
			$value = false;
		}
	}
	
	return $value;
}
add_filter("pmpro_registration_checks", "my_pmpro_registration_checks");

//swap the expiration text if the user has used the trial
function my_pmpro_level_expiration_text($text, $level)
{
	global $current_user;
	
	//has user used trial level already.
	if ( $current_user->ID )	{
		$used_trial = get_user_meta( $current_user->ID, "pmpro_trial_level_used_{$level->id}", true );

		if ( ! empty( $used_trial ) ) {
			$text = "You have already used up your trial membership. Please select a full membership to checkout.";
		}
	}
	
	return $text;
}
add_filter("pmpro_level_expiration_text", "my_pmpro_level_expiration_text", 10, 2);

This recipe is included in the blog post on "Offer Trial Memberships That Can Only Be Used Once" at Paid Memberships Pro here: https://www.paidmembershipspro.com/offer-trial-memberships-that-can-only-be-used-once/