Custom button on Lead form ribbon is not visible

Hi,

I used the Ribbon Workbench 2016 to add a new custom button to the form ribbon in the lead entity, but I can seem to get the button actually published to the form. I followed this instruction step by step and do not get any errors when publishing. But when I open a Lead record the button won't show up in the ribbon. 

Does anyone recognize this problem?

Thanks!

Kind regards,

Tim