Test api server to receive and return value from HTTP method.
Postman Echo API is a free Data Validation API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Details from postman-echo.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
US address standardization, congressional and state legislative districts, Census data; free tier
Validate EN 16931 e-invoices: XRechnung, ZUGFeRD, Factur-X, Peppol BIS
The Postman Echo API is provided by Postman (postman-echo.com).
Yes. The Postman Echo API is listed in the Data Validation category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Postman Echo API requires no authentication, so you can start making requests without signing up.
CORS support for the Postman Echo API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Postman Echo API is served over HTTPS, so it's safe to use in production.