Dial-in participants from Cameroon can't join the conference

I am doing a test of a conference call, but it is challenging for other participants to join the call from Cameroon. The number provided for Cameroon seem not to be working. How can this issue be solved? Is it because I am still using a trial version?

We are working on this issue and apologize for inconvenience. For now your participants can join via our website or Free Conference Call mobile/desktop app.