Can anyone help with a checkout redirect code issue in Dawn?

[KALEL1]

I'M TRYING TO ENTER A CODE FOR A CHECKOUT REDIRECT, BUT THIS MESSAGE APPEARS:
Liquid syntax error (line 663): 'endform' is not a valid delimiter for if tags. use endif
I DON'T KNOW WHAT TO DO, CAN YOU HELP ME

[Tristram]

Can you reply with a copy of the section of code that you've entered into the page?
Its basically saying that you have a line that looks like {% if ....something %} but after that further down the code, at some point there should be a corresponding {% endif %}