HTTP Request to an unsecured server


I am trying to use the HTTP request wizard to make REST calls to an API. I first tried to get authentication key by using POST Method. The serve is an unsecured address so there is no certificate details. Everytime I attempt I get the following error -

The underlying connection was closed: could not establish trust relationship for the SSL/TSL secure channel.

I have tried using postman and turning off the Certificate required option and it works. Can anyone help please? Many thanks in advance.