Why am I getting the error: "Invalid document template: Found 'ELSE' without a matching IF field"

This error has to do with your template. Something about an IF/THEN conditional statement that is built incorrectly.

This article describes how to build IF/THEN conditional statements. Confirm that the statement in your merge matches the syntax described in the article. This video has other tips about proper merge field formats.

Here are a couple specific things to check:

Make sure that you use straight quotes, rather than curly quotes in your IF/THEN statement. You can perform a browser search to better understand straight quotes. This article has more details.
As described in the video above, it's important to make sure that the text in the merge field is the same when you inspect the 'internal' label.