Shopify and Webshipper are tightly connected and will not work if some of the main components are inactive.
When picking items in Pio app, if you get an error message saying: "Something went wrong. Order not found" when completing the order, you can check this:
Log in to your Webshipper account and go to Connect > Order Channels > Shopify.
In the top menu bar, you will find the status of the connection with Shopify. This should always show as green and "Synchronisation".
If the integration is set to "Paused", Pio will not be notified about the new Shipment Orders (Webshipper orders) and it is missing it to dispatch.
How to fix if the integration is paused?
Go to Connect > Order Channel > Shopify > click "Edit order channel" in upper right corner.
Switch the dropdown back to "Synchronisation". 
Remember to click "Update order channel" to save the changes.
If you experience issues with printing the shipping labels, we recommend reading Webshipper: Label not printing
You can read the complete setup guide for Webshipper + Shopify integration here: How to integrate with Webshipper