Making a field(Receipt flag) read only based on another field(if attachment is uploaded)

Summary:

In a expense page, requirement is to make field1:'Receipt Missing' checkbox read only when field2:'receipt/attachment' is attached for that expense.
We tried to achieve this using sandbox: For 'Receipt Missing' component properties we gave read only expression : '#{bindings.IsAttachmentExist.inputValue !='Y'}' but this is not working.

• Had any done similar type of requirement

• Is if possible to achieve this requirement using sandbox

Any one knew any alternate solution to achieve this?

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