We’ll need some more information.
Okta uses JWTs for ID Tokens and for Access Tokens. Typically, you would use an ID Token as identity verification in your app for proof of login and SSO. You obtain these tokens through once of the standard OIDC/OAuth 2.0 flows.
Typically, you would use an Access Token to call your backend APIs and it would serve as an authorization assertion.
You can use Access Tokens to hit the /userinfo endpoint to get additional information about a user from Okta.
If that’s what you’re trying to do, then you would use a POST from postman with an Authorization header that passes in the Access Token. Like this (pseudo code):