You can dialback a caller as the helpline number. If the caller leaves a voicemail there is a PIN that is stored for each call and visible in the admin portal under the voicemail section.
You would call your helpline number and push
9 from there you will be prompted for a unique PIN that will connect you with the caller.
sms_dialback_options is enabled some SMS messages will have information about the PIN and a special magic link for dialing back.
Set the following options:
1) when a volunteer receives an incoming call SMS
static $sms_dialback_options = 1;
2) when a voicemail notification SMS is received.
static $sms_dialback_options = 2;
3) Or for both options to be set:
static $sms_dialback_options = 3;