I am asked for a github token

By default github has API access limits set for anonymous access. In order to overcome these limits one has to create a github token, which could be done as described in:

I get a Composer\Downloader\TransportException

During the installation of OXID eShop Professional or Enterprise Edition you get the following error:

Invalid credentials for '', aborting.

You may have stored some outdated or wrong credentials. Please review <your home directory>/.composer/auth.json and delete the section, which begins with “” resp. “”

I am asked “Do you want to remove the existing VCS (.git, .svn..) history? [Y,n]”

In general you can say “Yes”. It is not normally important to keep VCS history locally. You can always look it up on github.

There was an error during the execution of the unified namespace generator

If the generation of the unified namespace classes fails, OXID eShop will not run properly. In this case you should look here for possible fixes.