I have a Samsung A5 phone from Fido with wifi calling enabled, no problem. My partner has the identical phone not from Fido and when we enabled wifi calling it said he's not eligible. He has all other requirements, monthly plan etc.. It is really needed as the signal is poor in this area, the nearest tower is about 5km away. So why can't he get the same service?
Welcome to the community!
The reason why it is not working is that the phone was not purchased from Fido, VoLTE and WiFi calling was only supported on phones bought from Fido.
Fido has since allowed Grey Market devices from the Samsung Galaxy S8 and above, iPhone 6 and above, LG G8 thinQ to work with VoLTE but WiFi calling is not supported.
Many users were able to get both VoLTE and WiFi calling to work after speaking to a technician and having their IMEI numbers registered on the system.
Sine your phone is older that get Galaxy S8 but it still is a phone that Fido supports it would not hurt to get in touch with a technician and see if it can be added but there is no guarantee it will work.