Dynamic hidden text field generator, blank pop-up

I want to generate a hidden dynamic field populating the current user’s ID … but the generator is just showing a blank pop-up screen (Chrome and Internet Explorer, Windows 7 64-bit).
Nor can i find any documentation on the plugin anywhere …

I’ve already tried the following:
[dynamictext your-id "CF7_get_current_user_id"]
But without result.

Any help on the matter would be much appreciated.

https://wordpress.org/plugins/contact-form-7-dynamic-text-extension/