To list with Nembol you need to use a flat shipping policy.
Indeed, If you have set it to calculated, eBay will not know where your inventory is located and the listings will fail. Once you set the shipping to “Flat” you should be able to post.
However, you can still use a calculated shipping policy, by listing with Nembol using a flat shipping policy and then bulk editing the shipping policy once the products are on eBay.
To use a calculated shipping policy, all you need to do is:
Set your shipping policy as Flat > after you bulk listed all your products with Nembol > open your my eBay, and:
Open your listings
Bulk select them > click on bulk edit > shipping policy
Select calculated > apply
It should work only with the Buy it now listings with weight and dimensions info in their product card.