Hi @Shilpa Invents
Thanks for the question and using MS Q&A platform.
I understand that you are not using any DNS service (like Azure DNS or any other third-party DNS provider) and you have purchased your domain from SquareSpace, you will still need to manage your DNS settings through SquareSpace to point your subdomains to the appropriate Azure resources.
For additional information refer the below document to Set up a custom domain in Azure Static Web Apps:Set up a custom domain with external providers in Azure Static Web Apps | Microsoft Learn
reference:
deploy multiple websites to Azure Web App and have custom DNS address for each website - Microsoft Q&A
Custom domains with Azure Static Web Apps | Microsoft Learn
I hope this information is helpful.