Assign Tableau Next User Permissions

All users who view the embedded insights in your web app must exist in your Salesforce org and have the Tableau Next Consumer permission set. The Tableau Next Consumer permission set provides view access to Tableau Next insights. If your users aren't also Salesforce users with Tableau Next view access, they can't see the insight visuals in your web app.

For information on adding permission sets to users, see Assign a User a Tableau Next Permission Set

Next - Generate the Access Token and Frontdoor Url for Tableau Next Embedding