With apps situations like this you need to go to the app developers for app specific support, documentation and setup.
There's very little others can do as they don't have access to your stores settings and not the apps settings.
An apps developer is linked to from that apps page on the app store.
You can also try the shipping forum https://community.shopify.com/c/payments-shipping-and/bd-p/payments-shipping-fulfilment
Probably might just want this post moved there.