teamviewer works only in 1 way

Nobus

i just did a fresh windows 10 install on a Dell 790 USFF system for my brother.

he had a couple of problems, so i wanted to contact him with TV, as usual.

when i put in HIS ID - nothing happens - no error - nothing.

we retried several times, verified the ID etc....

i tried to get him to contact me - that worked without problems

what can be the cause of this strange behaviour?

we both have TV 15

Thanks in advance !

nobus