This is a very common issue that will, at some point, affect all Tradebox users who have an eBay channel set up. Roughly every 18 months, eBay revoke the authorisation that allows Tradebox to access your eBay data and it will need to be renewed.
The download of orders from eBay will stop completely, and a message will be displayed in the Tradebox issues log that tells you the eBay token has expired.
To renew it, go to the Channels page and double click on the affected eBay channel. You'll see your existing token displayed on the Details page. To the right of this, you'll see an arrow. Clicking on this will bring up a pop up box in Tradebox - ignore this for the time being as clicking ok too early will cause the process to fail - and also open up an eBay login page.
You'll be asked to log into eBay, and once logged in, you'll see the following message:
Clicking Agree confirms that Tradebox still has your permission to access your eBay data. Once that's gone through to the next page, you can close the browser window down.
This will take you back to the pop up box that appeared earlier in Tradebox.
When you click ok on this box, Tradebox will generate a new token which will allow it to connect successfully to eBay once more. On the next download cycle, orders from eBay will start appearing again as normal.