Hi @Jig Thakkar,
Welcome to Microsoft Q&A forum.
Please try here: Visual Studio Professional Subscription($99.99 user/mo, paid annually).
If you still fail to purchase Visual Studio Professional standard with Azure DevOps Basic Plan, please kindly try to contact Visual Studio Subscription team from here: Visual Studio Subscription Support - Visual Studio(scroll down => click "Visual Studio Sales, Account, Subscription and Billing Support" => Select country/region ... => check the detailed support information).
They should guide you and purchase Visual Studio Professional standard with Azure DevOps Basic Plan successfully.
Feel free to let me know if you have any further concerns :)
Have a nice day!
Tianyu*****
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