Hi,
Congrats with your elite package ! I think what envato means with custom job is a custom enquiry, take as example this is “job” that Unipen offers https://studio.envato.com/explore/logo-design/3150-professional-logo-design-3-different-initial-concepts you will be able to use your voucher on that page but Unipen also has a custom job section here https://studio.envato.com/account/users/16155/enquiries/new and I think that you won’t be able to use the voucher there.
Please note that I am not 100% sure about this but it is just what I think Envato meant.
I hope this will help you out 