How to send data from front end react js to backend node js using router.post

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Elasticsearch version: 7.17.20

Server OS version: MAC Pro

Kibana version (if relevant): 7.17.20

Browser version (if relevant): Chrome Version 124.0.6367.92 (Official Build) (arm64)

Browser OS version (if relevant): MAC Pro

Describe the issue:. In regards to https://search-guard.com/writing-kibana-plugins-part-4/

Topic : Calling Elasticsearch in a Route Handler - How to send data from front end react js to backend node js using router.post ?
i.e. How to pass the formdata object of values collected from Rendered application DOM (public/components/app.tsx) to Server side(server/routes/index.ts) as body of router method

Steps to reproduce:
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Expected behavior:

Provide configuration:
elasticsearch/config/elasticsearch.yml
elasticsearch/plugins/search-guard-7/sgconfig/sg_config.yml
kibana/config/kibana.yml (if relevant)

Provide logs:
Elasticsearch
Kibana (if relevant)

Screenshots (if relevant):

Errors in browser console (if relevant):

Additional data: