Forcing to change password when using API

Hello, we are working on creating installer for our software on DO through: https://github.com/seven1m/do-install-button

And it all works great up to the one point, when installing send-mail it runs into this error:

Setting up sendmail-base (8.14.4-4.1ubuntu1) … You are required to change your password immediately (root enforced) chfn: PAM: Authentication token is no longer valid; new one required adduser: `/usr/bin/chfn -f Mail Transfer Agent smmta’ returned error code 1. Exiting. dpkg: error processing package sendmail-base (–configure): subprocess installed post-installation script returned error exit status 1

So most probably chfn triggers the need for password change, as it is the first time login (even though from API launched script).

Any ideas on how to overcome it?