Register new users in a home server when registration has been disabled. More information: https://manned.org/register_new_matrix_user.
register_new_matrix_user --config {{path/to/homeserver.yaml}}
register_new_matrix_user --config {{path/to/homeserver.yaml}} --admin
register_new_matrix_user --config {{path/to/homeserver.yaml}} --user {{username}} --password {{password}} --admin