I follow these steps to get access token using post man. for v3
1. Loginto https://app.constantcontact.com/pages/dma/portal/
2. create app and generate secretcode
3. make below request through browser after changing client_id
4. Enable f12 for browser debug mode it will show the url in debug mode
something like https://localhost?code=Btm-DfwTesRXTplmOCEGpBI6CTD_GTL1FPclEAEt
5. Open PostMan and select request type as Post and make the below request after changing the Basic Auth and code parameter
Im getting this json error message.
"error_description": "unable to parse Authorization header javax.security.auth.login.LoginException: HTTP Basic username has invalid content com.pingidentity.common.security.InvalidInputException: Value for parameter \"Authorization\" is invalid. Value doesn't match regular expression: .*",
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