@Renaud MARGUERITTE Thanks for reaching out and apologies for delay.
Please make sure you have AAD premium P2 license in your tenant, followed by checking the account permission required for SSPR writeback :
Follow this to make sure you have correct account permissions : https://learn.microsoft.com/en-us/azure/active-directory/authentication/tutorial-enable-sspr-writeback#configure-account-permissions-for-azure-ad-connect
Do complete this checklist and confirm if you have followed the same : https://learn.microsoft.com/en-us/azure/active-directory/authentication/tutorial-enable-sspr-writeback#enable-password-writeback-in-azure-ad-connect
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