Function that returns upsells of products that grants access to a user's WooCommerce Membership plan

membership-product-upsells.php

<?php

function get_year_group_upsells() {
	$user_id = get_current_user_id();
	$args = array( 
		'status' => array( 'active', 'pending-cancellation' ), // Add or remove other statuses if you want
	);
	
	// Get user memberships
	$active_memberships = wc_memberships_get_user_memberships( $user_id, $args );

	if ( ! empty( $active_memberships ) ) {
	    $membershipPlansArray = array();
	    $upsellIDsArray = array();
	    
		// Get user membership plans
		foreach( $active_memberships as $membership ) {
			$membershipPlansArray[] = $membership->plan;
		}
		
		// Get user membership plan product ids
		foreach( $membershipPlansArray as $membershipPlan ) {
			$productIDsArray = get_post_meta( $membershipPlan->id, '_product_ids', true);
			if ( $productIDsArray ) {
					
					// Get product upsells
			    foreach( $productIDsArray as $productID ) {
            		$productUpsellsArray = get_post_meta( $productID, '_upsell_ids', true );
            		if ( $productUpsellsArray ) {
            		    $upsellIDsArray = array_unique( array_merge( $productUpsellsArray, $upsellIDsArray ));
            		}
            	}
			}
		}
	} else {
	    $upsellIDsArray = false;
	}
	
	return $upsellIDsArray;
}

?>