DDNS name 'my_name.airdns.org' is invalid

[Brilantdon 0]

Hello. I am a beginner in Air VPN. Achieved to forward a port successfully.
But when I decided to use the DDNS feature, I am constantly getting this error:
DNS name 'my_name.airdns.org' is invalid Only the following characters are allowed "abcdf....9-"
Can someone help me ? 
Do I have to set somewhere else the DDNS name and then use it here or what ?  

[OpenSourcerer 1359]

5 hours ago, Brilantdon said:

DNS name 'my_name.airdns.org' is invalid Only the following characters are allowed "abcdf....9-"

You do realize the error message tells you what is wrong?
Use a dash - instead of an underscore _.

[Brilantdon 0]

Yes I tried like 50 different names, without using the underscore "_".
But still not working. I don't know why

[OpenSourcerer 1359]

1 hour ago, Brilantdon said:

But still not working. I don't know why

Same error or something different?

[Brilantdon 0]

Yes, the same error is appearing repeatedly.
I tried just letters, letters combined with numbers but
still keeps showing the same error.

[OpenSourcerer 1359]

What's your OS and keyboard configuration? Maybe you're typing in the wrong charset?