Combined postage rule not being applied.

[thesaborco]

New to eBay.

Trying to offer a flat postage across the store.

Set a rule to subtract postage cost if more than 1 item is purchased.

But the rule is not being applied.

eBay  customer rep suggest the buyer will use request invoice function but this function is counter intuitive and not available on apps 

I see other stores reduce postage costs for additional items so I am pretty sure there is a way to do this.

Anyone?