So I'm setting up Spock to automatically push changes from the production server to a private github repo.

But somehow I'm getting this error:

[2019-04-02 08:55:38] production.ERROR: Spock command exited unsuccessfully:
Command: git push
Output: No output
Error:
warning: push.default is unset; its implicit value has changed in
..... some info over Git 2.0, probably not of interest now :) ..... 

Host key verification failed.^M
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

As the user running the website is www-data, I created a ssh-key in /var/www/.ssh (rest assured that dir is not used as the webservers-html directory :) )

I copied the public ssh-key into the repo's settings/keys tab; making sure to give it read AND write access.

But I still get the

Host key verification failed.^M
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists

Anybody knows how to tackle this?