Marking a form submission as "paid"

Is there a way that the admin of the Jotform account can mark a form submission as paid?  I want to use your system to keep track of reimbursement payments.

I don't want the form user to see the paid field, just the admin. 

I would like to recommend you to add a single choice element to your form and then hide it from your users. 

After you add the single choice element, please right-click on the field and then select the "Hide" option. By this way, this field won't be able to display in the form. 

Then go to "My Forms" section and click on the "View Submissions".

Click on the "Edit" button.

Write your own note to the submission and then click on the "Submit" button. Please note that the user won't be informed about this process except for the admin of the form.

Here is the final result: