I've created a custom header that works fine. I replaced Magento's cart, and instead added a shopping basket icon in the header. Like so:
When pressed it redirects to the cart.
I followed the suggestion here: Magento 2 Get Cart Quote Total in minicart.phtml
<span data-bind="html: getCartParam('subtotal')"></span> in the HTML but got an error
getCartParam is undefined
Any ideas where I'm going wrong?