Hi @Aimery Thomas ,
Great to know that it works now and thanks for sharing the update here.
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others.". and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
[Get page custom webparts]
Issue Symptom:
Graph API: /sites/{sitesId}/pages/{sitePageId}/webparts throwing the following error after a custom SPFx webpart to the page:
"code": "One of the provided arguments is not acceptable",
Current status:
The issue has been resolved after trying it again a few hours later. The reasons could be either, service temporarily unavailable for maintenance / is overloaded / changes made on the page took time to reflect.
Hope this helps.
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