Diana here from the Shopify Support Team.
I'm not personally super-familiar with the ins and outs of the App itself, but do you happen to have the pre-requisites required to use the Multivendor Marketplace App's shipping option? I was doing some poking around and found this blog article on Webkul's website that seems to imply that in order to get the shipping set up, you have to have two things:
If you don't have both of those enabled, then the shipping feature isn't available to you. I can't speak for the Gold Plan (Webkul can likely offer more insight on that), but if you're curious about adding on Shopify's advanced carrier-calculated shipping to your plan, you can talk to any of my colleagues on the Guru Team to discuss your options!
Hope this helps! :)
The app we develop, Advanced Shipping Rules, allows you configure different rates for all your different vendors, it will give you access to assign different carriers to each group and input unique ship from zip codes. You can also use flexible rule based rates for other vendors as well.