How to change Woocommerce vendor address during Cart/Checkout to use in Woocommerce Tax calculations?

Question

Is there a way to alter the address WooCommerce Tax uses for the tax nexus using a filter/hook upon loading the cart and checkout pages? We tried (see below) and it didn't work.

We are using a WordPress plugin for WooCommerce called WC-Marketplace (WCMp) to create a multi-vendor platform that allows vendors in our market to sell goods. Everything works as expected except for taxes. We only want to charge sales tax if the vendor and the customer reside in the same state. I understand this sounds like a product specific question but we have reason to believe it needs to be handled with code that's specific to WooCommerce.

https://wc-marketplace.com/

Example of what we want: Vendor is in Ohio, Customer is in Ohio = Sales tax applied Vendor is in California, Customer is in Ohio = No tax applied

We're using WC Tax to automatically calculate sales tax within the USA. However, it seems to be using the address found in WooCommerce > Settings > General on the admin dashboard instead of the actual vendor's address configured in their WCMp dashboard which is stored as an entry in the wp_usermeta table.

https://woocommerce.com/products/tax/

Example: Vendor is in California, Customer is in Ohio = Behaves as if Vendor is in Ohio as our general settings are configured to Ohio in this scenario.

We reached out to WCMp support and the way we they put it to us, we'll need to write code to intercept the tax calculation ourselves. We believe it's possible to do this using an filter/hook and override it with the correct address before taxes are calculated.

After reading through WooCommerce documentation and code itself, here's code I wrote to accomplish this:

//
// Change tax location to use vendor location
function custom_woocommerce_order_get_tax_location( $args, $instance ) {
    global $woocommerce;

    // Get vendor based on product ID
    $vendor_id = '';
    foreach( WC()->cart->get_cart() as $cart_item_key => $cart_item ){
        $post_obj    = get_post( $cart_item['product_id'] );
        $post_author = $post_obj->post_author;
        $vendor_id = $post_author;
        break;
    }

    if ($vendor_id) {
    // Set tax location based on vendor
        $args = [];
        $args['country']    = metadata_exists( 'user', $vendor_id, '_vendor_country' )  ? get_user_meta($vendor_id, '_vendor_country', true):'';
        $args['state']      = metadata_exists( 'user', $vendor_id, '_vendor_state' )    ? get_user_meta($vendor_id, '_vendor_state', true):'';
        $args['postcode']   = metadata_exists( 'user', $vendor_id, '_vendor_postcode' ) ? get_user_meta($vendor_id, '_vendor_postcode', true):'';
        $args['city']       = metadata_exists( 'user', $vendor_id, '_vendor_city' )     ? get_user_meta($vendor_id, '_vendor_city', true):'';
    }
    
    return $args;
}
add_filter('woocommerce_order_get_tax_location', 'custom_woocommerce_order_get_tax_location', 10, 2);

In short, the above recurses through items in the cart and gets the WCMp vendor's ID based on which WP user created it (always the vendor). It then uses the vendor_id to get the address metadata from the wp_usermeta table and override the woocommerce_order_get_tax_location filter's $args.

This is the code for that filter, get_tax_location()

https://woocommerce.github.io/code-reference/files/woocommerce-includes-abstracts-abstract-wc-order.html#source-view.1524

I believe this is working to some extent as when I print out the WC Object, we see in the WC_Customer Object that the correct vendor's State and Zip Code are listed as so:

[changes:protected] => Array
(
    [shipping] => Array
        (
            [postcode] => 90003
            [city] => Los Angeles
            [address_1] => 
            [address_2] => 
            [state] => CA
        )

)

Unfortunately the tax is still being calculated as if our business is the tax nexus and not the vendor.

What is the correct way to intercept and change the vendor address WC Tax uses before the cart and Checkout pages load the taxes?

Thanks a million!