Welcome to the Community, we are so happy to have you here with us.
This error will most likely need to be something you need to reach out to support directly to fix, but there is a step that you can try before reaching out. I would recommend reconfiguring your selling channel and attempting a store refresh as this will likely be the first thing support will have you attempt anyways.
Navigate to Settings(wrench icon) > Selling Channels > Store Set up > 'Connection next to that selling channel and follow the prompts. Once this is complete you will want to attempt another refresh of this selling channel.
If this does not work, contact support and let them know that you have already attempted a store reconfiguration but it did not fix the error.
Please let us know how it goes either way.
-Erin: Your Friendly ShipStation Community Manager