Hi @southafrican ,
Based on the formula you provided, I think there is something wrong with it. The second argument of the Text function is required to type a CustomFormat formula, but you typed a Currency.
Please consider modify your formula as below:
Set the Default property of the Budget (F19/20) Text Input box to following:
Text(displayItem.'Last Approved PLF Value (FY19/20)', "[$-en-US] ##,###")
or
Text(Value(displayItem.'Last Approved PLF Value (FY19/20)'), "[$-en-US] ##,###")
Please consider take a try with above solution, then check if the issue is solved.
Best regards,