Zapier is a 3rd party platform that offers a free plan but will require a subscription for a better experience.

Zapier offers a few options available as triggers from GetResponse:

Where the resulting action is an invitation from Trustpilot. 

You should try to match the Trustpilot configuration to your own settings on Trustpilot.

If you don't see any invitations in the queue or the Zap shows any errors, reach out to support@trustpilot.com