How to Resolve Azure AD Connect Event ID 611 Error: Password Synchronization Failed

How to Resolve Azure AD Connect Event ID 611 Error: Password Synchronization Failed. The following error is flagged on the Azure AD Connect Server.

Event ID: 611 (Log: Application, Source: Directory Synchronization)
Level: Error
Computer: AAD.contoso.com
Description: Password synchronization failed for domain: contoso.com.
Details: Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsException: RPC Error 8453 : Replication access was denied. There was an error calling _IDL_DRSGetNCChanges. at
Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsRpcConnection.OnGetChanges(ReplicationState syncState) at
Microsoft.Online.PasswordSynchronization.DirectoryReplicationServices.DrsConnection.GetChanges(ReplicationState replicationState) at
Microsoft.Online.PasswordSynchronization.RetryUtility.ExecuteWithRetry[T](Func`1 operation, Func`1 shouldAbort, RetryPolicyHandler retryPolicy) at
Microsoft.Online.PasswordSynchronization.DeltaSynchronizationTask.SynchronizeCredentialsToCloud() at
Microsoft.Online.PasswordSynchronization.PasswordSynchronizationTask.SynchronizeSecrets() at
Microsoft.Online.PasswordSynchronization.SynchronizationExecutionContext.SynchronizeDomain() at
Microsoft.Online.PasswordSynchronization.SynchronizationManager.SynchronizeDomain(SynchronizationExecutionContext syncExecutionContext)

Permissions were missing from the local Azure AD sync account.

Replicating Directory Changes
Replicating Directory Changes All

Resolution

Assign the missing permissions by using the ACL editor.

Open the Active Directory Users and Computers snap-in;
On the Security tab, click Add;
In the Select Users, Computers, or Groups dialog box, select the local Azure AD sync account, and then click Add;
Click OK to return to the Properties dialog box;
Click the local Azure AD sync account;
Click to select the Replicating Directory Changes and Replicating Directory Changes All check box;
Click Apply, and then click OK;
Close the Active Directory Users and Computers snap-in.