Connecting your Magento 2 store to ShipStation requires steps in both ShipStation and Magento. Following the instructions included below (which are also outlined in the Magento 2 connection modal)
Go to your Account Settings (the wrench icon in the upper right).
Next, select Selling Channels and then Store Setup from the sidebar on the left.
Then, click on the Connect a Store or Marketplace button and select Magento.
Use the drop-down menu to select Version 2.
Download the module linked in the first step, and extract the contents to your Magento Folder on your server.
Log into your Magento Admin as the Administrator user.
Click System on the left, then Cache Management under Tools.
Select Flush Magento Cache.
Click System, and choose Web Setup Wizard from the left navigation panel.
Select Component Manager and continue with Manage Your Components.
Go to the Auctane_API module from Listing and select the Enable option from the Actions column.
Click Next. We recommend making a backup of existing Code, Media, and Database files. Click Enable.
Go to System > All Users to create a new admin user for ShipStation.
This step is optional but recommended so that your new integration keeps working even if you change your primary admin password.
Click Add New User and fill out all of the required fields.
Enter your Store URL, new Administrator Username and Password into the corresponding fields in ShipStation.
NOTE: The Store URL can be found in Stores > Configuration > General > Web > Base URLs (or Base URLs (Secure) for http configuration)
If you use any custom statuses, change them from the defaults during the connection process in ShipStation (as shown in the image below).
You can also add your Warehouse Location Attributes, choose the weight unit you use for your store, and select when Magento will invoice.
Finally, click Connect
You can now make any store setup adjustments you wish and start importing orders from Magento!
NOTE: If you have Multiple Stores on your Magento 2 account...
Each one can be connected separately to your ShipStation account. You will need to set the Store View in Magento (near the top-left corner of your Magento admin site) to the store you're reviewing before looking at the Store URL value. Then, simply use the store's unique URL along with the Username and Password from the earlier steps. Repeat this process for all of your stores.