Snapshot restoration is failing

I used this plugin before without any issues but can’t seem to get my snapshot to work right now. I want to move a site to another server and I get the following error message:

“An unknown response returned from Snapshot backup attempt. Aborting. Double check Snapshot settings.”

First I exported a full snapshot (including all files and all db tables) from the original site, then I uploaded it via FTP to the uploads/snapshots folder of the new WordPress-installation. Then I imported the snapshot through blank directory URL under Import and finally I clicked restore with all files and all tables. But this is not working.

Which steps am I missing?