Hi,
Presuming your "short_description" field is within the same schema as your expression and you are not trying to reference a field from a Dataset you should be able to use:
if short_description == "How do I cancel?" then "0270c251c3200200be647bfaa2d3aea6" elsif short_description == "I'm having an issue" then "c54de838d7b122004f1e82285e61036b" else end
If you can avoid it I would remove the apostrophe from your text string of "I'm having an issue" just to rule out any special character problems.