Hi,
What shopping cart module are you using? As you may have noticed, MaterialMart comes with a dropdown shopping cart module, called "Flexible - Dropdown Shopping Cart". It is optional to install this module along with MaterialMart.
If you are using that module;
- Make sure install and publish this plugin: "Flexible - Virtueamart 3 Dropdown Shopping Cart - Plugin"
If you are not using it (maybe you already have your own shopping cart module)
- Make sure unpublished this plugin: "Flexible - Virtueamart 3 Dropdown Shopping Cart - Plugin"
Regards.