Gaelle
I am now fixed and working. I put the solution at the bottom of my problem thread
Your picture suggests that your components are not communicating well rather than there being something structural wrong (On that thread you can see I had keychain and access problems - I needed AppleCare for a bit of help with those)
What you need to do is delete your ebay user details from the GS>Preferences>accounts menu and close GS down.
Then open up your Keychain access utility (mine was in an applications>utilities folder on the mac)
Look down the login list for eBay tokens (default or otherwise) and delete them. Then re-open GS and go back to the GS>Preferences>accounts section and use the + button on eBay account to open the eBay login page. Sign in with user name and password, then check to see if it has added your email address for PayPal payments. I can’t remember if this came through automatically or if i typed it in, but suddenly the Paypal error ! mark started to disappear. you can test by selecting a listing and using verify.
Good luck