App Store Connect Api Certificates

Hi, I am working on the App Store Connect Api. I have problem with the creation of Certificates. Here is the snapshot of my code for Access Token and reference for certificates.

https://developer.apple.com/documentation/appstoreconnectapi/create_a_certificate

When i try using Postman, i got this error. Is my implementation wrong? If so, please help to guide me on this. Thank you.

App Store Connect Api Certificates
 
 
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