This permission should be added to all Profiles that need to enable the Einstein Activity Capture.
Note: The default standard System Administrator profile should have 'Manage Lightning Sync' activated by default.
The permission 'Manage Lightning Sync' can be enabled from the Salesforce Classic and Lightning Experience both however, Einstein Activity Capture can be enabled only from Lightning Experience.
Salesforce Classic: Setup | Administer | Manage Users | Profiles | Select your Profile and ensure that "Manage Lightning Sync" and "Manage Users" are enabled.
Lightning Experience: Click the Gear icon | Setup | Users | Profiles | Select your Profile and ensure that "Manage Lightning Sync" and "Manage Users" are enabled.
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