When you are adding / revising channel settings for your eBay channel, and you sign in to your eBay account to authorise ChannelUnity, you receive the following error message:
There was an error passing information between the third party you just came from and eBay
This can be caused by an expired browser cookie which needs to be refreshed.
Please sign out of ChannelUnity and close your browser.
Clear your browser cookies, and in a new browser window, log into ChannelUnity again and try to repeat the above process.
You should now be able to authorise your eBay account as expected.