Custom Webhook to index documents

I would like to index some trigger variables into Elasticsearch using custom webhook (POST). I used below configurations:

1. Using Route53 DSN

Host: Route53_DSN_For_Elasticsearch_Cluster
Path: test-index/_doc

I tried to test it using “Send test message”, and I got following error:
UnknownHostException: Name or service not know

2. Using AWS Elasticsearch VPC endpoint

Host: VPC_Endpoint_For_Elasticsearch_Cluster
Path: test-index/_doc

I got following error:
java.io.IOException: Failed: HttpResponseProxy{HTTP/1.1 403 Forbidden

3. Using 127.0.0.1 or localhost

Host: 127.0.0.1
Path: test-index/_doc

Got compilation error on Host regex :
Invalid Host

I was able to successfully use POST to index documents using Postman client in both case 1 and case 2. But, getting errors when I tried to replicate into Alerting. Please help me in resolving this issue so I can index docs using custom webhook.

Anyone, please help ?