They already use etoro
They sign in with etoro. You connect that account to the account they have with you.
They do not have an etoro account
You create their etoro account, then open etoro for them already signed in.
They already use etoro
The person is an etoro customer. They come to your site and sign in with etoro. You learn who they are, and you connect their etoro account to the account they already have with you. You do not create a new etoro user in this path.
The calls for this path are listed under Partners API in the sidebar. If a step fails, look up what you see in Troubleshooting.