createInvoice()
getInvoices()
Invoice subject is an object that has invoices (contact or estimate)
createInvoice() : \Moneybird\Invoice
\Moneybird\Invoice
getInvoices(\Moneybird\Invoice\Service $service, string $filter) : \Moneybird\Invoice\ArrayObject
\Moneybird\Invoice\Service
string
\Moneybird\Invoice\ArrayObject