Yes, you have to pay for a retake.
Here is a list of FAQs:
https://www.microsoft.com/en-us/learning/certification-exam-policies.aspx
When you are ready to retake the exam, schedule an appointment as you normally would. Note that you must pay for each exam you retake and follow Microsoft’s retake policy.
Thanks,
Sam Lester (MSFT)
https://blogs.msdn.microsoft.com/samlester/
Twitter - @SQLSamLester
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