Hi @Tavi
Ah OK I understand what you mean - so when customers place an order on your store, they have to pick a shipping company/shipping method right?
You would actually define the name and price of the shipping rates on your Shopify store. So for example, you could simply have 1-2 rates and call them ‘Standard Shipping’ and ‘Priority Shipping’ or something along those lines. You don’t necessarily need to define the exact shipping company, because you will be placing the order on behalf of the customer via your dropshipping app.
I realise you are not using Oberlo, however there’s a great article here on setting up shipping settings when dropshipping that I would recommend checking out. It would most likely apply to other dropshipping apps also, and it explains the various considerations to take regarding shipping.
You also mentioned cash on demand - do you mean the cash would be collected from the customer upon delivery? This might be trickier to set up, as it depends on if the dropshipping suppliers provide this type of payment option. For that sort of setup, I would recommend reaching out to the third party dropshipping service support directly, as they should be able to provide more context on that.