This is a classic firewall issue. Go to Windows Firewall and manually allow zoiper.exe for Private and Public networks. Also, disable any SIP ALG on your router.
Zoiper 3.15 Free Download: Top Features and Installation Guide zoiper 315 free download top
To ensure security, it is highly recommended to download Zoiper only from the official Zoiper website or verified app stores. Программа ZoiPer для Windows - Novofon.com This is a classic firewall issue
If you are looking for a lightweight, "no-frills" dialer that simply works, Zoiper 3
due to its stability and lower resource consumption compared to newer builds. Core Features of Zoiper 3
Supports TLS, SRTP, and ZRTP for secure communication.
are now available, many users still swear by the streamlined performance and legacy features of the Zoiper 3.x Key Features of Zoiper 3 Free SIP & IAX Support