* Go to **Support menu » Developer » API Explorer**.
* Set *Entity* to **Invoicegen** and *Action* to **Generate**.
* Enter a billing period in the following format: "2019-2"
* First number is the year; second is 1 for Jan-Jun, 2 for Jul-Dec.
* Optionally, select **Add Parameter** and select a single contact ID. If you don't, all timebanks eligible to receive an invoice in this billing period will receive one (unless it already exists).