Misses the matching field area

Hi,
I installed your free plugin, I created a gravity form, I set your plugin configuration succesfully, I uploaded a pdf file with fields, I see it in the merge form but I get no matching fields, the matching area is empty.
I don’t see any field neither from gravity form neither from pdf.
I see only the two labels: Gravity Field Name and PDF Field Name
If I click on add columns nothing happens.
Any tips?