Hosted Vault vs HCP - difference wrt application integration

We have a nodejs application that was storing secrets in a self-hosted vault service using KV store. We used the vault root token to access the vault service and were able to read and write.
For production, we moved to HCP - cloud version and changed the endpoint which is configured as publicly accessible and are trying to use the root token in a similar fashion but our Application is unable to access the vault and the root token keeps expiring… What is the mistake or additional change required to be done ?

You should never be using the root token.

Instead you should use one of the many auth methods (such as AppRole) to fetch a token whenever you are needing to access Vault.