After merging with Sharelatex, Overleaf evolved, they will charge for the feature of integration with Github and direct git access in the future.
Finally, the git integration in Overleaf v1 was a free feature during its long beta period, and we will continue to offer it for free to all users with Overleaf v1 accounts. For users who sign up after Overleaf v2 is out of beta, GitHub sync and direct git access will be available on our paid plans, like on ShareLaTeX. As with many other v2 features, this means that the owner of the project will need a paid subscription in order to connect their project with GitHub or enable direct git access, but their col
Source: Working Offline in Overleaf – Overleaf, Online LaTeX Editor
Working Offline in Overleaf – Overleaf, Online LaTeX Editor