Can't pass verification

I’m unable to pass the verification step. I tried in two different websites, each one associated with an Analytics account linked to the corresponding Webmaster Tools account.

Steps:
1) Go to Settings > Google Publisher Plugin
2) Click on the “Get started” button
3) Check that the current account is ok
4) Click on the “Verify” button

Expected behaviour:
The plugin shows a page related to Google AdSense or something like this.

What happens instead:
The plugin shows the “Get started” page again.

May this be due to a conflict with other plugins?

https://www.ads-software.com/plugins/google-publisher/