@Alena Stanchyts Welcome to Microsoft Q&A Forum, Thank you for posting your query here!
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Plan 1:
Could you please open the Azure portal and navigate to your Azure AI Language resource and open the language studio and check if that works?
Plan 2:
Please confirm if you have either Owner or Contributor access on the resource.
Also ensure that you have Cognitive Services Language Owner
RBAC roles on your resource. More info here.
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Plan 3:
Navigate to the Language studio Select the settings icon and select the right resource
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Then navigate to the Custom text classification
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Hope this helps. If you have any follow-up questions, please let me know. I would be happy to help.