API Only Users Can Access Only Salesforce APIs (Critical Update, Enforced)
Where: This change applies only to Lightning Out.
When: This critical update will be automatically activated when your sandbox or production org is upgraded to Spring ’20. Since auto-activation doesn't happen on one specific date for all orgs, you can ignore the Auto-Activation Date listed on the Critical Updates page in Setup.
Who: This change affects users with the API Only User permission.