Ansible provisioning ERROR! Using a SSH password instead of a key is not possible

Create a file ansible/ansible.cfg in your project directory (i.e. ansible.cfg in the provisioning_path on the target) with the following contents:

[defaults]
host_key_checking = false

---

^{provided that your Vagrant box has sshpass already installed - it's unclear, because the error message in your question suggests it was installed (otherwise it would be "ERROR! to use the 'ssh' connection type with passwords, you must install the sshpass program"), but in your answer you add it explicitly (sudo apt-get install sshpass), like it was not}

I'm using Ansible version 2.6.2 and solution with host_key_checking = false doesn't work.

Adding environment variable export ANSIBLE_HOST_KEY_CHECKING=False skipping fingerprint check.

This error can also be solved by simply export ANSIBLE_HOST_KEY_CHECKING variable.

export ANSIBLE_HOST_KEY_CHECKING=False

source: https://github.com/ansible/ansible/issues/9442