Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
You wanted to know how to allow access to Port 9999.
I suggested that your VM should accept traffic on Port 9999 in addition to our Platform allowing the traffic on Port 9999.
You were able to make the Port 9999 listen inside your OS and post this, you confirmed the issue has been resolved.
Kindly let us know if this helps or you need further assistance on this issue.
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