Hello Jareth Lomson,
Thank you for reaching out to Microsoft Support!
After our test, when the folder name is v1.0, it runs well, and the test results are as follows:
Please try again, or use the id of the item to get the children, as follows:
Reference document:
https://learn.microsoft.com/en-us/graph/api/driveitem-list-children?view=graph-rest-1.0&tabs=http
Hope this helps.
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