Hello PAUL CHONG CHUANG YONG,
Thank you for posting in Q&A forum.
You can try to add the Administrator or Administrators group or Enterprise Admin group in root domain to Root domain PC and Child Domain and Child Domain PC and Ext Domain and Ext Domain PC.
I hope the information above is helpful.
If you have any questions or concerns, please feel free to let us know.
Best Regards,
Daisy Zhou
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