Likely the issue is related to the sitewide issues that others are experiencing for the last two days.

If you are having trouble signing in but you are able to reach the community and you are signed in here, try using the link in the upper right to reach your My eBay page by clicking on your profile picture icon.

Try another browser or a private or incognito browser window to rule out a browser or cookie issue.

If you are having problems making a purchase, wait a bit and try again later.

https://downdetector.com/status/ebay/