@Narender Kumar Welcome to Microsoft Q&A forum and thanks for reaching out here.
As per the error message ""Unauthorized tenant: Target subscription id<123> tenant <123> is not in allowed list." It seems like your snowflake is different subscription and different tenant than that of Synapse Workspace tenant and subscription. Could you please validate this?
- If they are in different tenant, then please ensure that the provider subscription or tenant has registered Microsoft.Network .
- In case if both the resources are in different subscriptuons and have different vNets, then you will have to peer the vnets as described in this SO post - Cross-subscription Private Endpoint in Azure
Kindly validate these steps and let us know how it goes.
Hope this info helps.