iOS: Incoming Call Audio not on loud speaker

When my iOS app receives an incoming call and that call is answered, the audio stays only on the device speaker and not on the loud (hands free) speaker. That is, I need to hold the device up to my ear to be able to hear the remote audio. This only happens for incoming calls as when I make an outgoing call, the remote audio defaults to the loud (hands free) speaker.

I am calling  ServicesManager.sharedInstance()?.rtcService?.forceAudioOnSpeaker() to see if I can force the audio onto the speaker but this call has no effect.

How can I get the audio from an incoming call to be on the hands free speaker?