Why am I not able to make calls via VoWiFi even though I am connected to a WiFi network?

Permanently deleted user

There are a few possible reasons:

VoWiFi requires an adequate Wi-Fi signal strength (with a minimum bandwidth of 25 kbps) before initiating the automatic connection to WiFi Calling. You can try to move to an area where the signal strength is stronger.
If the WiFi network has a captive portal (Eg. Starbucks which requires a login), you may have to launch the browser and sign in to the network with the provided username/password.
For public WiFi networks, the provider may have policies in place to block WiFi calling services.
For private WiFi networks (e.g. company WiFi), the location may have policies in place to block WiFi calling services.
Your device may not fulfil the prerequisites for Yoodo VoWiFi service.