Go to the field configuration - > storage section, select Alter and change dropdown to Text, this sets mysql database column to type that is not limited to 255 or 2048 characters as when VARCHAR(255) or VARCHAR(2048) are selected. Downside of text is that it is slower than when using varchar. You culd as well manually change column type to e.g. VARCHAR(5000), this number can go up to 65.000 but you need to do it manually (using e.g. PhpMyAdmin)