"You don't have access" errors stem from Looker Studio's dual permission model — you need access to both the report AND data sources.
Report Permissions
Click Share, verify email listed as Viewer. For wider sharing: "Anyone with the link can view."
Data Source Permissions
Most common issue. Resource → Manage Added Data Sources. "Owner's credentials" = only owner's access used. "Viewer's credentials" = each viewer needs separate access.
Embedded Reports
For embeds, viewers need Google account access OR set report to public with Owner's credentials.
Quick Fix
Switch all sources to "Owner's credentials" unless you need viewer-level control. Contact us for permission architecture.