El AL sends you the etick number with a blank after the first 3 numbers. So you copy paste with that in there. THen the check in says that only 13 characters allowed for etick number. It's tricky, it took me several tries till I got the issue.

Should be easy to remove any blanks from the number and then process or even give an error message that you got 14 characters, or better would be don't add the blank character in the email with the etick number.