Here the steps to set up the Automatic Feedback Service (AFS) with Sendgrid. Learn more about the AFS here. 

1- Find your Trustpilot's email address from Get reviews > Invitation Methods > AFS

2- You will need to whitelist and/or add Trustpilot to your SPF record: Add Trustpilot to your SPF record

3- Create a mail on Sendgrid with the script below which you will send to your Trustpilot's email address to trigger invitations: 

<script type="application/json+trustpilot">
{
"recipientName": "Dynamic placeholder",
"recipientEmail": "Dynamic placeholder",
"referenceId": "Dynamic placeholder"
}
</script>

Follow this guide if you want to use other structured data snippets to personalize even more your invitations (ex: send invitation in different languages, add product review invitations...): Add a structured data snippet for Automatic Feedback Service

4. From the email settings, select which template you want to send to your customers & add if needed an invitation delay. 

Now every time you will send the script to Trustpilot, an invitation will be created. You will see it from your Invitation history.