firebase-ios-sdk: Firebase fetchWithExpirationDuration completion handler not called

The callback isn’t received from “fetchWithExpirationDuration” API. The completion handler isn’t being called and hence, the remote config changes are not in effect.

    long expirationDuration = 3600;
    [self.remoteConfig fetchWithExpirationDuration:expirationDuration completionHandler:^(FIRRemoteConfigFetchStatus status, NSError *error) {
        if (status == FIRRemoteConfigFetchStatusSuccess) {
            NSLog(@"Config fetched!");
            [self.remoteConfig activateWithCompletionHandler:^(NSError * _Nullable error) {
               // [self.delegate configDownloadComplete];
            }];
        } else {
            NSLog(@"Config not fetched");
            NSLog(@"Error %@", error.localizedDescription);
        }
    }];