I'm trying to write a basic client side script that loops through every line, checks if the item has 'track landed cost' ticked and if not, applies withholding tax (WHT).

The reason is that we need to start accounting for WHT but tax law in the country in question only applies withholding tax for items that aren't physically shipped - so only on downloadable software, professional services, support contracts, etc.

Rather than ensure our accounts team manually applies WHT on every line correctly, I thought I'd make a script to do it automatically, ensuring they don't forget or get confused if an item is physically shipped or not.