How to Send Email to Contact and relate it to Case via Salesforce REST API?

Enable "Email-To-Case".


Path:
/services/data/v53.0/sobjects/Case/quickActions/SendEmail
 
HTTP Method:
POST

Body:
{    
    "contextId": "5008c00001Ejue0AAB"
    "record": {
        "HtmlBody": "<div+style=\"font-family:+Arial;+font-size:+14px;\">Test</div>",
        "Subject": "InfallibleTechie",
        "ToIds": ["0038c00002bkSPZAA2"]
    }
}
 
Example:
 


Output: