How to fetch data from a ACF field into Field in FluentForms?

Hi there, I have made a form for a postfeed update so I can change the status of an invoice. If not yet payed, I want to add an amount to the previous total pay. So when I choose the post from a post update field, I want to fetch the in an ACF field stored data of the previous total, so I can automatically calculate the new total amount and send that to a new ACF field.

Is that possible?