Hi, I did some digging in the code for the error message you get when trying to add the server and the pool code appears to be calling this url: https://trace2.ntppool.org/ntp/2003:a:157f:b76d::2
Which returns this error:
{“Op”:“read”,“Net”:“udp”,“Source”:{“IP”:“2604:1380:2:6000::15”,“Port”:59995,“Zone”:“”},“Addr”:{“IP”:“2003:a:157f:b76d::2”,“Port”:123,“Zone”:“”},“Err”:{}}
With my own IP I get this output:
{“Time”:“2020-05-19T21:36:08.130390579Z”,“ClockOffset”:261505,“RTT”:78756427,“Precision”:119,“Stratum”:1,“ReferenceID”:1347441408,“ReferenceTime”:“2020-05-19T21:35:54.039874817Z”,“RootDelay”:0,“RootDispersion”:1205444,“RootDistance”:40583657,“Leap”:0,“MinError”:0,“KissCode”:“”,“Poll”:8000000000}
Given the “test my NTP server” sites work fine, I guess the restrictions on your NTP server are too strict. There’s a page here with suggestions for how to configure. If that doesn’t help could you post the relevant lines from your ntp config file please.