Call drop outs and poor call Quality

Hi,

I'm new to this community and reaching out for advise.

We run a small business of 10 staff, all using the Rainbow app. For the past six months on a daily basis we either cannot pick up a call, unable to hear the caller, poor call quality or the call just drops out. Some users experience this issue all day and others have no problems at all.

Any advise or tips you can give would be very welcomed.