- Error Code 20400:

Short Message - Invalid request encoding. 

Long Message - Invalid request encoding. Please use utf-8 encoding and eliminate any non utf-8 encoding in request content.

Explanation and resolution:  

Typically this error is being returned when there is some data, that is not correctly encoded in the UTF-8 character set, that eBay require. Check first the general title, or ebaytitle for example if it is not ghosted and has a different and separate title filled in for that channel or any other fields, that might contain such characters and remove them. In some cases copying and pasting the title or text in WordPad or Sublimetext can show the hidden characters, that yield the particular error and this way they can be easily identified and removed before re-listing the item.