Hi, Can anyone explain about this error with an example would be better.
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https://docs.appian.com/suite/help/20.4/Expressions.html#passing-arguments
You may not mix both styles.
Yes this error will occur if you are missing a keyword such as below. If you are debugging a large form, try commenting out sections at a time until you narrow it down. Feel free to post some code for review here as well.
a!localVariables( local!data, a!textField( label: "Text Field", local!data /* <- missing 'value' keyword */ ) )