; https://hledger.org/invoicing.html
2020-02-01 * (201602ab) AB Inc. | invoice
    (assets:receivable:ab)      $1000
2020-02-15 * AB Inc. | payment for 201602ab
    (assets:receivable:ab)     $-1000  ; = $0  ; assert this if fully paid (optional)
    revenues:consulting:ab     $-1000
    assets:checking             $1000