Remove Products based on a specific product getting added.

remove_products_from_cart.php

<?php
function remove_products_from_cart( $cart_item_key ) {

// Products allowed with gift sub
	$allowed_products = array( 230973 , 231122, 230510 );

	// Gift Subscription Product ID
	$gift_product_id = 230973;

	// Lets get all the IDs in the cart
	foreach (WC()->cart->get_cart() as $value) {
		$cart_ids[] = $value['product_id'];
	}

	//Check cart IDs again gift product ID
	if ( in_array( $gift_product_id, $cart_ids )) {

		wc_add_notice(' Gift Subscriptions must be purchased individually. ');

		foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {

			$product_id = $cart_item['product_id'];

			if ( !in_array( $product_id, $allowed_products ) ) {

				WC()->cart->remove_cart_item( $cart_item_key );

			}
		
		}
	
	}

}
add_action( 'woocommerce_add_to_cart', 'remove_products_from_cart' );