Per collaborative editing function for Microsoft Office

Hi, I'm using Box for work as a guest collaborator of our client.
Today, I tried to use your collaborative editing function for Microsoft Office on the app for the first time, but I got this error message: "Disabled by Administrator."
I followed this page to enable it.
https://support.box.com/hc/ja/articles/5954058378899-Box-for-Microsoft-Office%E5%85%B1%E5%90%8C%E7%B7%A8%E9%9B%86%E6%A9%9F%E8%83%BD%E3%81%AE%E6%9C%89%E5%8A%B9%E5%8C%96%E3%82%AC%E3%82%A4%E3%83%89

As I mentioned earlier, my Box account is a personal account just for collaborating with my clients, and I obviously have no administrator in my organization.
I'm wondering who I should contact to obtain permission to use the collaborative editing function for Office in this situation.
I appreciate your support in advance.

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