Not compatible with PMPro v3.0 - Use Payment Plans Add On instead: https://www.paidmembershipspro.com/add-ons/pmpro-payment-plans/

pmpro_level_groups_pmpro_checkout_boxes.php

<?php //Do not copy this PHP tag into your code.
/**
  * Define groups of levels and allow members to select from both levels at checkout.
  * Useful for offering multiple pricing structures for membership (i.e. Monthly, Annually)
  *
  * Add this code below to your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
  */

// Define the groups of levels. array(1,2) means that levels 1 and 2 are in a group and options will be shown for both levels at checkout for those levels.
global $pmpro_level_groups;
$pmpro_level_groups = array( array( 1,2 ) );

// Show the "Select a Payment Plan" box with options at checkout.
function pmpro_level_groups_pmpro_checkout_boxes() {
	global $pmpro_level_groups, $pmpro_level, $discount_code, $wpdb;

	// No groups found? return.
	if ( empty( $pmpro_level_groups) || empty( $pmpro_level ) ) {
		return;
	}

	// Get the id for the discount code if available.
    if ( ! empty( $discount_code ) ) {
		$discount_code_id = $wpdb->get_var("SELECT id FROM $wpdb->pmpro_discount_codes WHERE code = '" . $discount_code . "' LIMIT 1");
	}

	// Get first group this level is in.
	foreach( $pmpro_level_groups as $group ) {
		if ( in_array( $pmpro_level->id, $group ) ) {
			// Show options for these levels. ?>
			<div id="pmpro_level_options" class="pmpro_checkout">
				<h3><span class="pmpro_checkout-h3-name"><?php esc_attr_e( 'Select a payment plan.', 'paid-memberships-pro' ); ?></span></h3>
				<div class="pmpro_checkout-fields">
					<div class="pmpro_checkout-field pmpro_checkout-field-radio">
						<?php foreach( $group as $level_id ) {
								$level = pmpro_getLevel( $level_id);

								// Apply discount code if available.
							    if ( ! empty( $discount_code ) ) {
								    $code_check = pmpro_checkDiscountCode( $discount_code, $level_id, true );
								    if ( $code_check[0] == false ) {
								       // Discount code doesn't apply to this level.
								    } else {
								        $sqlQuery = "SELECT l.id, cl.*, l.name, l.description, l.allow_signups FROM $wpdb->pmpro_discount_codes_levels cl LEFT JOIN $wpdb->pmpro_membership_levels l ON cl.level_id = l.id LEFT JOIN $wpdb->pmpro_discount_codes dc ON dc.id = cl.code_id WHERE dc.code = '" . $discount_code . "' AND cl.level_id = '" . (int)$level_id . "' LIMIT 1";
								        $level = $wpdb->get_row( $sqlQuery );
								        // If the discount code doesn't adjust the level, let's just get the straight level.
								        if ( empty( $level ) ) {
								            $level = $wpdb->get_row("SELECT * FROM $wpdb->pmpro_membership_levels WHERE id = '" . $level_id . "'");
										}
								        // Filter adjustments to the level.
								        $level->code_id = $discount_code_id;
								        $level = apply_filters( 'pmpro_discount_code_level', $level, $discount_code_id );
								    }
								}

								// Apply filters.
								$level = apply_filters( 'pmpro_checkout_level', $level ); ?>
								<div class="pmpro_checkout-field-radio-item">
									<input type="radio" id="pmpro_level_<?php echo $level_id; ?>" name="level" value="<?php echo $level_id; ?>" <?php checked( $pmpro_level->id, $level_id );?>>
									<label class="pmpro_label-inline" for="pmpro_level_<?php echo $level_id; ?>" /><?php echo pmpro_getLevelCost( $level, false, true );?></label>
								</div>
								<?php
							}
						?>
					</div> <!-- end pmpro_checkout-field-radio -->
				</div> <!-- end pmpro_checkout-fields -->
			</div> <!-- end pmpro_level_options -->
			<?php
		}
	}
}
add_action('pmpro_checkout_boxes', 'pmpro_level_groups_pmpro_checkout_boxes');

@kimcoleman, is this script still supported in PMP v3? It worked well prior to v3 but now it doesn't. Could it be updated? Thanks!

@hbcondo Payment Plans are now a part of this Add On: https://www.paidmembershipspro.com/add-ons/pmpro-payment-plans/ . We don't support the custom coded method in this gist any longer.

Thank you for your reply and letting us know. We found that using JavaScript to update this hidden input value appears to get this working again:

<input type="hidden" id="pmpro_level" name="pmpro_level" value="1">

Overall, it would be nice if this gist could be supported since Payment plans are not compatible with the built-in discount codes features of PMPro