Getting error as `"Token exchange failed for project ..."`

[kmonsoor]

I am getting this error while building & uploading this app to GAE. Tried enabling all the related API, custom domain etc. with no success.

╰─ gcloud app deploy app.yaml
Services to deploy:

descriptor:      [/home/kmonsoor/golinks/app.yaml]
source:          [/home/kmonsoor/golinks]
target project:  [personal-go-links]
target service:  [default]
target version:  [20210416t033010]
target url:      [https://personal-go.et.r.appspot.com]


Do you want to continue (Y/n)?

Beginning deployment of service [default]...
╔════════════════════════════════════════════════════════════╗
╠═ Uploading 0 files to Google Cloud Storage                ═╣
╚════════════════════════════════════════════════════════════╝
File upload done.
Updating service [default]...failed.
ERROR: (gcloud.app.deploy) Error Response: [9] Cloud build bf7fc46d-74db-4c93-82f8-2f4763d8aec7 status: FAILURE
Error ID: 792D3E61
Error type: BuildError
Error message: 15 Apr 2021 21:30:30 INFO     Running as user 0, group 0
15 Apr 2021 21:30:30 INFO     Arguments: ['--name=asia.gcr.io/personal-go-links/app-engine-tmp/app/ttl-2h:cdcb8c2b-6ef0-4cbb-b058-38724f97335f', '--src=/workspace', '--base=asia.gcr.io/gae-runtimes/python27:python27_20210322_2_7_RC00']
Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/bin/appender.par/__main__.py", line 90, in <module>
  File "/bin/appender.par/__main__.py", line 79, in main
  File "/bin/appender.par/containerregistry/client/v2_2/docker_session_.py", line 71, in __init__
  File "/bin/appender.par/containerregistry/client/v2_2/docker_http_.py", line 198, in __init__
  File "/bin/appender.par/containerregistry/client/v2_2/docker_http_.py", line 301, in _Refresh
containerregistry.client.v2_2.docker_http_.TokenRefreshException: Bad status during token exchange: 403
{"errors":[{"code":"DENIED","message":"Token exchange failed for project 'personal-go-links'. Access denied."}]}
Full build logs: https://console.cloud.google.com/cloud-build/builds/bf7fc46d-74db-4c93-82f8-2f4763d8aec7?project=943188903055

Any idea where I'm getting stuck?