You are registered in the UK, but you are currently posting on the US discussion boards.
Here are some things to try if you are having problems signing in to ebay.co.uk:
Try another browser. If you are able to sign in successfully, try clearing your cache ("for all time" if that is an option) in your original browser. Possibly try manually deleting eBay cookies as well. Maybe try clearing cache and cookies even if you cannot sign in using another browser. Or try a private or incognito browser window.
Sometimes when eBay changes something, the change can conflict with data in your cache or your cookies. Eventually the data will be overwritten with new data, but you can speed the process up yourself. Whether you have a problem depends upon the precise data you have stored, which is unique to each user.
If you erase your cookies when you close your browser, you will have to sign in and go through verification the next time you go to eBay. But erasing your eBay cookies manually when you are having a problem can help, particularly if the problem is a corrupt cookie.
Other things that can cause sign-in problems: VPNs, privacy software such as Ghostery or Disconnect, blocking cookies, blocking third-party cookies, using tracking protection, disabling JavaScript, blocking scripts, corrupt cookies, ad blockers. Try disabling those on the sign in page or temporarily, if possible.
Try going to the main eBay page and signing in there rather than relying on an old bookmark which may not be redirecting properly. If you have problems loading the main page, try the site map:
https://pages.ebay.co.uk/sitemap.html
Alternative sign in pages:
https://www.ebay.co.uk/signin/
https://signin.ebay.co.uk/ws/eBayISAPI.dll?SignIn
If you have previously signed in using a Google, Facebook or Apple account, try that again; it may work better for you. Take care not to accidentally create a new eBay account, though.
To rule out device issues, try another device.
To rule out network issues, try another network; try using a browser on your phone when not connected to your usual WiFi.
You may be able to sign in using the eBay app. If so you may be able to link a social media account to your eBay account, then sign in using a browser that way.
