Installation issues ubuntu

Dear community,

i have installation issues on Ubuntu 20.04. When i follow the guide on the github page i get the following problems:

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== Enabling default add-ons ==
== Installing dependencies ==
git@github.com:paper-trail-gem/paper_trail.git (at 1e56afd@1e56afd) is not yet checked out. Run `bundle install` first.
Don't run Bundler as root. Bundler can ask for sudo if it is needed, and installing your bundle as root will break this application for all non-root users on this machine.
Fetching git@github.com:paper-trail-gem/paper_trail.git
Warning: Permanently added the RSA host key for IP address '140.82.121.4' to the list of known hosts.
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

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

Retrying `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks --quiet` at /opt/dradis-ce due to error (2/4): Bundler::Source::Git::GitCommandError Git error: command `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks --quiet` in directory /opt/dradis-ce has failed.

If this error persists you could try removing the cache directory '/opt/dradis-ce'
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

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

Retrying `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks --quiet` at /opt/dradis-ce due to error (3/4): Bundler::Source::Git::GitCommandError Git error: command `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks --quiet` in directory /opt/dradis-ce has failed.

If this error persists you could try removing the cache directory '/opt/dradis-ce'

Retrying `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks --quiet` at /opt/dradis-ce due to error (4/4): Bundler::Source::Git::GitCommandError Git error: command `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks --quiet` in directory /opt/dradis-ce has failed.

If this error persists you could try removing the cache directory '/opt/dradis-ce'

Git error: command `git clone git@github.com:paper-trail-gem/paper_trail.git /usr/share/rvm/gems/ruby-2.7.2/cache/bundler/git/paper_trail-1099ff99be89c52753a9da60941c019b052529ab --bare --no-hardlinks
--quiet` in directory /opt/dradis-ce has failed.

If this error persists you could try removing the cache directory '/opt/dradis-ce'
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