Removing free product when cart doesn't contains product of particular category.

functions.php

<?php

/**
 * Removing free product from cart when cart doensn't contains product of perticular category.
 */
function remove_product_from_cart() {
    
    // Run only in the Cart or Checkout Page
    if ( is_cart() || is_checkout() ) {

    	$product_category_id 	= 73; // ID of category       
        $prod_to_remove     	= 2115; // Product ID of Free Product
        $cart_contains_category = false; // Default set to false : This means cart doesn't contains any product of perticular category
        $free_pro_cart_id 		= "";
        
        foreach ( WC()->cart->cart_contents as $prod_in_cart ) {
            // Get the Variation or Product ID
            $prod_id = ( isset( $prod_in_cart['variation_id'] ) && $prod_in_cart['variation_id'] != 0 ) ? $prod_in_cart['variation_id'] : $prod_in_cart['product_id'];
            $product_cats_ids = wc_get_product_term_ids( $prod_id, 'product_cat' );

            if ( in_array( $product_category_id, $product_cats_ids ) ){
            	$cart_contains_category = true; // cart has the product of particular category.            	
            	break;
            }
        }
        
        if ( !$cart_contains_category ) { // remove free product if cart doesn't contain product of perticular category
        	$free_pro_cart_id = WC()->cart->generate_cart_id( $prod_to_remove );
            // Remove it from the cart by un-setting it
            unset( WC()->cart->cart_contents[ $free_pro_cart_id ] );             
        }
    }
}
add_action( 'template_redirect', 'remove_product_from_cart' );