sorry for the bad english.
Do you have notifications for Facebook Messenger enabled in Settings?
Your English was fine.
yes everything is on. do you receive calls when the app is closed?
Yes. Try checking your notification settings on the Facebook website. If that doesn't work try reinstalling the app.
I did all that, but I also tested with some of my friends iPhones and None of them worked either, they only receive the call with the app opened on background
I believe this is usual behaviour. Apps like Skype, WhatsApp, etc cannot receive calls when not opened in the background.
Why not leave it open?
he said whatsapp works with it closed.
i have no idea really, but pure speculation would be that it's easy to have multiple facebook accounts that you can sign in and out of on multiple devices. therefore if you have it closed, which account are you using? how does it know whether to ring on your device?
with whatsapp your account is locked to your phone number, there is a much more 1:1 relationship between accounts and phones, accounts and people. (although i'm sure not always). therefore it can be fairly certain it can ring on the phone you have linked your account to.
is it an issue to leave it open?
hello. i just want to understand why this happens. so a have facebook messenger and whatsapp installed on my iphone 5s. heres the problem, i can only receive facebook calls when the app is open or running in the background, when using whatsapp i can have the app closed on the multitask and i can receive a call with no problem. i have tried enabling background app refresh and still this continuous. is this normal? why would facebook messenger have a call feature if to only works when the app is running? and why does whatsapp witch is owned by facebook doesn't have the same issue?
sorry for the bad english.
Don't close apps using the app switcher if you don't need to. It doesn't offer any benefit.