@TomRobinson-8577 Azure AD Connect: 1.5.30.0 and Windows Server 2019 Standard also support password writeback.
I assume by Microsoft 365 Standard & Microsoft 365 Premium, you are referring to Microsoft 365 Business Standard and Microsoft 365 Business Premium. If that is the case, you are good with required licenses. If you have Office 365 Business Premium, that doesn't include password writeback feature for synced accounts as only Azure AD Premium P1 or P2 and Microsoft 365 Business include password writeback features. Refer to https://video2.skills-academy.com/en-us/azure/active-directory/authentication/concept-sspr-licensing for more details.
When you are resetting the password, have you confirmed if you are complying with On-prem password policies? E.g., if the minimum password age is 1 day in on-prem AD and you have synced a newly created user account whose password is not 1 day old, you'll get error.
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