The server has responded with response code 502 error

hello, I just moved from mailpoet 2 to 3 and I am getting an error “An error has happened while performing a request, the server has responded with response code 502” and my previous newsletters doesn’t show up in my newsletter list. Also I cannot edit or create new newsletters, only shows a blank page. https://screencast.com/t/nk2Ijp8c

Already tried debugging, resetting, disabling all other the plugins etc. Mailpoet 2 works fine.

Using wpv4.9.1

hope you could help us out or this could be a bug in mailpoet3.

The page I need help with: [log in to see the link]