Not able to Import certificate bundle

I created a root CA and intermediate ca and tried uploading them using the /config/ca option.
the imported_issuers and imported_keys are showing Nil. What could be the issue?
ca-chain-bundle.certs.pem file contains the intermediate ca and root ca.

vault write arytest/$CUST_ICA_ID/config/ca pem_bundle=@ca-chain-bundle.certs.pem 
WARNING! The following warnings were returned from Vault:

  * This mount hasn't configured any authority information access (AIA)
  fields; this may make it harder for systems to find missing certificates
  in the chain or to validate revocation status of certificates. Consider
  updating /config/urls or the newly generated issuer with this information.

Key                 Value
---                 -----
imported_issuers    <nil>
imported_keys       <nil>
mapping             map[57e66960-74fe-4672-2663-4d81c140a9e5: 9a7bd720-e37f-1c5a-cb72-48811c9f5ccf:]

The docs (PKI - Secrets Engines - HTTP API | Vault | HashiCorp Developer) imply that the config/ca endpoint should be provided with a certificate and private key.

As you don’t mention submitting a private key, I guess that may well be the problem.

Thanks @maxb for the reply.
Which Private key do i need to include? All the CA chain private keys? including root?

No, only the private key for CAs that Vault is going to be operating.