Aws-amplify integration with React Native Token - unauthorized - react-native

Question

I have configured my React Native application to use a Cognito user pool that is used for user identity management and authentication using AWS Amplify. I am using Custom Authentication for user management. I am able to register, log in and perform other user management-related tasks. I also have an API gateway and a few Lambda Functions which I want to access through my React Native app. When I sign in, I receive a JWT Token which I want to send to the API gateway to access my Lambdas, but no matter what I do I get an 'unauthorized' 403 or 401 message from my API Gateway.
My question is: How can I expose the API gateway/ Lambdas to the Cognito user pool users and Why the token generated by Cognito itself is unauthorized to access my api gateway.
P.S. - I used postman with the right Auth URL and settings, the postman token itself is authorized to access the API gateway and lambdas. (The user credentials are the same as I use with the React Native app)
I have spent a few days, any pointers in the right direction would be very helpful.
Thanks in advance.
NPN
Amplify Config:
const awsmobile = {
aws_project_region: 'us-XXXX-X',
aws_cognito_region: 'us-XXXX-X',
aws_user_pools_id: 'us-XXXX-XXXXXX',
aws_user_pools_web_client_id: 'XXXXh1i5nXXXX',
//aws_user_pools_web_client_secret: 'XXXXXoofuu0lXXXX',
oauth: {
domain: 'XXXXXXXX.us-XXXX-X.amazoncognito.com',
scope: ["email", "openid", "aws.cognito.signin.user.admin"]
},
aws_cognito_username_attributes: ['EMAIL'],
aws_cognito_social_providers: ['GOOGLE'],
aws_cognito_signup_attributes: ['XXXXX', 'XXXXX', 'EMAIL', 'XXXXXX'],
aws_cognito_mfa_configuration: 'OFF',
aws_cognito_mfa_types: [],
aws_cognito_password_protection_settings: {
passwordPolicyMinLength: 8,
passwordPolicyCharacters: ['REQUIRES_LOWERCASE', 'REQUIRES_UPPERCASE', 'REQUIRES_NUMBERS', 'REQUIRES_SYMBOLS'],
},
aws_cognito_verification_mechanisms: ['EMAIL'],
};
export default awsmobile;
import { Auth } from 'aws-amplify';
const login = async (username: string, password: string) => {
const response = await Auth.signIn(username, password);
console.log(response.data.signInUserSession.accessToken.jwtToken);
return response;
};