By default in the Billing for FusionPBX in-app software, the Offline plugin is not configured. You need to set up some default settings in order to let it work.
Please add the following default settings:
|billing||offline.debug||boolean||false||Turn on more debugging messages in the Syslog or journal system|
|billing||offline.enable||boolean||true||Enable or disable this plugin.|
|billing||offline.postpay_capable||boolean||true||Enable this plugin for post-paid customers.|
|billing||offline.prepay_capable||boolean||true||Enable this plugin for pre-paid customers.|
Remember this is a manual payment plugin. Your customer will try to add money, and he will send his willing-to-pay notification. After that, he will send you the proof of payment, when you are 100% positive you got your payment, you will need to release the money and it will be automatically applied to his balance.