They said:

"To set up the OAuth server in una.io, you have to create an OAuth client in it. Could you please confirm if you did it yourself or the una.io support team did it for you?

You also need to specify your WordPress site URL as origin URLs in the bx_oauth_allowed_origins table so that we can make SSO requests from your WP to una.io

Also, please check what grant_types you have specified while creating an OAuth client. You can refer to this document to proceed."

https://github.com/unaio/una/wiki/Dev-API