You have a link in an email that worked correctly in the email previewer, but once the email is sent, the link does not work. You may get an error such as HTTP error 414 when clicking on the link from the email.
This error means that the URL is too long, possibly due to the MKT_TOK being added to the URL link, and therefore the URL is reaching the length limitation. This limitation is set by the admin of the website the link points to. Either disable the token added to the link or contact your website admin in order to increase the URL limitation.