Error login into sharepoint site settings > Plumsail Actions pack

Hi everyone

I've just installed the workflow actions pack trail this morning and followed the instructions as given. Everything went alright untill i needed to configure a default account to start the workflows. I went to site settings on my subsite where i wanted to deploy my workflow and clicked on "Plumsail Workflow Actions Pack" in the "Site Administration Section". When i open this i get a screen to login to, here i enter the login and password of my SharePoint online environment but i'm getting following error message that i can't explain:
"Can't connect to site: Cannot contact site at the specified URL https://url.... There is no Web named xxx "


I'm the SharePoint administrator and I'm sure my password is correct.
I've already did some research but i can't find a solution.
I would be very thankfull if someone could help me out with this.