Hi  

It looks like there are some requirements to check first:

• Unity AI Gateway is enabled for your account. <- if you're enterprise, Beta previews are Off by default. An account admin can toggle this on in the account console.
• The billable usage system table needs to be enabled for your account. (find out more in first link below)
• The Unity AI Gateway Budget Public Preview needs to be enabled in the account console. 

Hope this helps.

References:
https://learn.microsoft.com/en-us/azure/databricks/ai-gateway/budgets-beta
https://docs.databricks.com/aws/en/ai-gateway