Vertex AI endpoint response contains HTTP error

Using Vertex AI and custom container image, I imported a flask application (written in Python) and successfully created an active endpoint. The code runs fine locally and provides response. However, when I use Postman to access the endpoint and pass the json input, I keep getting the following error:

Bearer realm="", error="invalid_token"

and sometimes I get a HTTP request error. Used the google authentication code and included it in Postman -> Authorization -> Bearer Token.

Am I missing out on something? Need help in resolving the error..

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