Problem with Image Button plugin

Good afternoon,
I cannot setup the image for the image button plugin.
After I select the image type (by clicking the related radio buttons “link template” and “details page”) I click “save setting”.
The gear on the “save setting” button start to turn…and never stop!

If I come back in the same page nothing is saved…

How can I solve it?

Thank you!
Federico
PS: looking the instruction on the page https://www.wpdownloadmanager.com/download/wpdm-image-button/ is wrote “Select (just click) a button image” … but if I click on the button and not on the radio button nothing happen…