TextNow "choose area code" - dose not work with NextDns - why?

Hi,

this may be niche question for only one of you use application TextNow.

in short this app allow to call Us free of charge over internet.
you choose your own number (from list they give you) and its free.

be default my phone internet is through NextDns address 

i have notice that when i am connected to NextDns i get an error from the TextNow app in the "choose area code" screen - how do i know its NextDns? - i turned of the DNS setting in my phone and the problem solved.

now , when i am connected to NextDns - i dont see any block message in the logs...

so i dont know what blocking option i use disable this (i use full parental control blocking with NextDns and Hagezi multi pro (i think)

the wired thing is that after i did choose the area code - i have full access to the app...

any suggestion what in my NextDns block "parts" of the app?

thank you

ps - i dont want every time for choosing the "area code" to disable the Dns setting in my phone - because its my child phone and the setting is locked ( so i can rest assure that all his surfing is protected via NextDns)