Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi Hasssan,
To better help you, I'd like to know what client you are signing in to it with Office 365.
As far as I know, when signing into Office 365, for example, signing/connecting to Outlook Web App (OWA) or Outlook client, there is no need to install or mange SSL certificate. As a result, there is no option to manage the SSL certificate in the Office 365 Admin Portal. This is because the related Office 365 certificate has been issued and added into the trusted center by the certificate authority.
As for your situation, can you confirm if you can singn into OWA or Outlook client (if you have no the client you can sign into OWA instead) to see if you can sign in it successfully. This is to identify if your Office 365 service is good or not.
Regards,
Alan