Need to make invoice header DFF read only after the invoice is paid

Summary

Need to make invoice header DFF read only after the invoice is paid

Content

Hi All,

For one of our clients, we have enabled Invoice Header DFF and we are capturing a couple of values which will be used during payments process. Once the payment is made, if we open the invoice, we can still see the invoice header DFF is editable. We want to disable the edits by making it ready only. 

We tried to do through personalization using expression language, but i cannot find any binding parameter for payment status flag. There are other columns like remaining amount or due but none of these are working.