When publishing pixels, a user is asked to enter a URL along with the description of the URL (My link text). You may notice that the link text is limited to 255 characters.
In the newer versions of the software, the link text was made unlimited. If you have an older version of the software, you will need to modify the database table 'blocks' to make the field unlimited.
The best way to do this is with phpMyAdmin. Log in to phpMyAdmin and locate the blocks table. Click on the 'change' symbol for the alt_text field. Then from the 'Type' column, select 'TEXT' from the dop-down list and click save.
(PhpMyAdmin is a MySQL database administration tool which is available on most services offered by various hosting companies. You can use this tool to manually manipulate the database & do database backups (export), and restore database backups.)