Cannot reset password because guest agent is unavailable

[nd1012]

I use automatting scripts to create and setup Debian 10 server unattended. After creating a server, the script connect with SSH and the user is requested to set a new password. But my script needs to execute shell commands directly after the login - so the password change request is disturbing.

A workaround is to reset the server password, because when doing this manually, the password change prompt won't appear when logging in with the generated password, and it's possible to access the shell directly. But this seems to work manually with the Cloud API web interface only:

When I want to execute the Servers::resetPassword method, I get an error for a new created up and running server:

Code: guest_agent_unavailable
Message: Cannot reset password because guest agent is unavailable

Now I don't know if this is a server image misconfiguration, or I need to wait until the guest agent is available, or how I can determine from a script (maybe using the Could API?) when/if the guest agent is available? Or is there a solution to change the initial password from a PHP script using ssh2 without the need to use Servers::resetPassword? Fact is, I never logged in to the server and I never uninstalled the guest agent.

I use the server image 5924233, server type 9 and data center 4.