A template variable is a supported placeholder, such as {{Case.case_number}}, that resolves to case data during generation.
Keep the braces, spelling, punctuation, and capitalization intact. Do not invent a placeholder based on a screen label. For example, the long due-date field is {{Case.due_on_long}}.
A text field, formatted list, table collection, URL, and embedded image produce different results. Select the format that fits the section you are building.
Previews respect your permissions. A blank value may mean the case has no source data or you cannot access it. It does not always mean the placeholder is invalid.
Review legacy-variable notices and use current equivalents when updating templates. Run another test after changing placeholders.