Concourse git-prs error run check step: check: resource script '/opt/resource/check []' failed: exit status 1

Question

Concourse pipeline has below git-prs resource

- name: git-prs
  type: pull-request
  source:
    repo: ((repo.id))
    uri: ((repo.uri))
    access_token: ((repo.access_token))
    private_key: ((repo.deploy_key))
    only_mergeable: true

Getting error as

git-prs errored run check step: run check step: check: resource script '/opt/resource/check []' failed: exit status 1 stderr: failed to unmarshal request: json: unknown field "only_mergeable"

If I comment only_mergeable then getting the error in private_key step as

git-prs errored run check step: run check step: check: resource script '/opt/resource/check []' failed: exit status 1 stderr: failed to unmarshal request: json: unknown field "private_key"

Please note that this was working fine till 22-Jan-2024. No changes done in Pipeline after that as well no change in keys. I assume no expiry date for Private key as well. Let me know what I am missing here? Concourse version - 6.7.6