POST Request for creating Tyk Policy fails

Thanks for sharing the config file.

I think you need to change your config file to set a path rather than a resource file. You can modify the config file but a much better way would be to use environment variables

{
...
  "policies": {
     "policy_source": "file",
    "policy_path": "/mnt/tyk-gateway/policies"
  },
}
- name: TYK_GW_POLICIES_POLICYPATH
   value: /mnt/tyk-gateway/policies

Kindly remember to call the hot reload API after calling the policies create API.

Let us know how it goes