@Aurélie EHANNO ,
I have covered your telephone number for the security of personal information. Thanks for your understanding.
What is your environment? On-premises, online or hybrid?
Do you enable the room account for use with Skype for Business?
Try to run Enable-CsMeetingRoom cmdlet to enable it.
If your environment is not purely on-premises, it needs to change the settings on-premises. Then, it will be sync to online.
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