In-Place archiving not working as expected

Hi, I have a mailbox ie user@domain.com which is nearly full and I have policy called "MRM Policy 1" under compliance management/retention policies with a retention tag of "default 6 months move to archive". The user has in-place archiving enabled, the "MRM Policy 1" is applied to the user under mailbox features/retention policy. For some reason the messages older than 6 months (and there are messages older than 6 months) are not moving automatically to the online in-place archive. The mailbox retention hold is false, I have checked this with powershell. I also ran the managed folder assistant in powershell to force the archiving, but it is not happening. I waited for 2 days, still nothing. I raised a technical support ticket with Microsoft where the support engineer told me that Office 365 Business Premium subscription does not do archiving and need to switch to either Microsoft 365 Business or Microsoft 365 Enterprise E3 plans.
I am also told that you can get online archiving as an add-on for our Office365 Business Premium plan, but when I follow the Microsoft provided link ( https://docs.microsoft.com/en-us/office365/servicedescriptions/exchange-online-archiving-service-description/exchange-online-archiving-service-description#exchange-online-archiving-plans) , it refers to an add-on for on-premises exchange servers. We run our email completely in the cloud. This other article states that Office 365 Business Premium does the in-place archiving. What Microsoft is telling me conflicts with this article that was answered by a Microsoft engineer.
Here is the link to the article: https://answers.microsoft.com/en-us/msoffice/forum/all/does-o365-business-premium-now-include-in-place/5ca0216b-e649-4c2b-b073-54e51f5023b7

I am confused. Can someone shed some light?

Thank you

Best regards

Alfred56