KubernetesManifest createSecret fails with illegal base64 data at input byte 4329 in Azure DevOps pipeline execution

I am trying to deploy an application into Private AKS cluster using Azure Devops pipelines in VMSS agent.

I have create service connection with kubeConfig option ( saved without verification ) for connectivity.

Task:

- task: KubernetesManifest@0
      displayName: create secret
      inputs:
        action: 'createSecret'
        kubernetesServiceConnection: PRIVATE_AKS_SC
        namespace: 'default'
        secretType: 'dockerRegistry'
        secretName: 'mysecret'
        dockerRegistryEndpoint: 'PRIVATE_ACR_SC'

Error:

Same task works for Public AKS cluster.