To connect your OpenCart store with ShipStation follow the steps below.
1) Download the ShipStation extension from the setup page when you go to add your OpenCart store to ShipStation.
Head 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.
2) Using an FTP program (we’re using Filezilla for this example), extract the shipstation and admin folders to the root level of your OpenCart folder.
Make sure that you append the contents of the admin folder rather than overwriting any existing data.
*Changes to an FTP server's files cannot be easily undone, so we recommend creating a backup of your information before making any changes, just to give yourself peace of mind.
3) Modify the permissions (chmod) on your config.php file to 777.
To do this in Filezilla, right-click the config.php file and choose "File Permissions." Then, just change the number to 777.
4) Sign into your OpenCart admin site, go to Extensions, and then go to Modules.
5) Find the ShipStation line, and click Edit.
6) If there are no keys in the two fields, make sure that you generate new ones, and then Save.
7) Keep the key page open as you'll need to copy both the ShipStation Key and ShipStation Verification Key into the app.
8) Go back to your ShipStation account and choose to add an OpenCart store, if you haven't already. Here, enter the ShipStation Key and ShipStation Verification Keys you copied, and the URL for your store.
9) Test the connection.
10) If you use any custom statuses, change them while you're setting up your store in ShipStation.
When you're done click Finish to fill in the rest of the information for the store and you have set up your OpenCart store in ShipStation!