Hi, @Ventrapragada Kiran Kumar Welcome to the Microsoft Q&A platform, thanks for posting the question.
As we understand the ask here is you want to create TABLESPACE in Azure PostgreSQL.
Unfortunately, this feature is not supported in AzurePostgreSQL. Since you do not have access to the storage of Azure Database for PostgreSQL Flexible Server and you cannot attach additional disks.
Can you share what is the cmd you tried to understand better?