In your Freshcaller account, you need phone credits to buy numbers or make and receive calls.
Please note that only Account Admins can access the Billing Section and add phone credits.
Login to your Freshcaller account.
Go to Admin Settings > Billing section.
To recharge, click the Add credits button and choose the credits that you want to add. An easier option is to enable the auto-recharge option. By default, the auto-recharge option is disabled. (It is to be noted that auto recharge is not available when you are in trial)