@Heidi Mao Welcome to Microsoft Q&A forum! We are sorry to hear that you are facing issues with ADT access.
Were you able to access it earlier? Please note that the user should have the right permissions. To give a user permissions to manage an Azure Digital Twins instance, you must assign them the Azure Digital Twins Data Owner role within the instance.
If a user attempts to perform an action not allowed by their role, they may receive an error from the service request reading 403 (Forbidden). For more information and troubleshooting steps, see Troubleshooting: Azure Digital Twins request failed with Status: 403 (Forbidden).
Also, I suggest you take a look at the documentation to know more about Securing Azure Digital Twins
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