i got same issue, postman web version cannot send request to localhost. . So i'm just use desktop version of postman and it works

Postman Website cannot send a request to your computer's localhost. It first needs to connect to your PC with the Postman desktop client. You can download it here. Run it, then go to the Postman workspace in your browser -> send the request and it will work.

The Error is pretty much clear here. Cloud Agent Error: Can not send requests to localhost. Select a different agent.

Postman web version cannot able to send requests to the server that runs on your local PC(localhost). In order to send a request to the localhost URL, you need to install Postman desktop client.

I also faced the same issue recently. Just use the postman desktop app and after sign in, post/get etc. requests can be executed without a problem.