Hi @Peter Mc
Welcome to Q&A forum ~
But your issue is related to license requirement, which is not suppported on Q&A forum. Thanks for your understanding.
If possible, it is recommended to contact your Licensing Solution Partner for confirmation..
The following information is my persional results of an online search.
Here is a PDF "Licensing Microsoft Office software in Commercial Licensing", the images below are taken from it. And the images mainly describe the licensing requirements that users need to edit documents on Office web or Office Online Server.
Please note, Office 365 ProPlus is renamed to be Microsoft 365 Apps for EnterPrise.
Hope the information is helpful to you.
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