Check the Invoice number generated automatically. If you have the administrator rights (CRM/full access), you can change the number format clicking the Change format link next to the Invoice number field and entering the necessary prefix and number format in the fields of the opened Change format window.
The Invoice Date, i.e. the date the invoice was issued, is set to the current one, by default. If necessary, you can change it selecting it from the calendar, or entering it manually in the following format dd/mm/yyyy.
To set the Due date, i.e. the date by which the invoice needs to be paid, use one of the available options on the right: Due on receipt, 15 days, 30 days, or 45 days, or select it from the calendar, or enter it manually in the following format dd/mm/yyyy.
Select a Language for your invoice from the Invoice language drop-down list. If your language is not yet present in the list of the available ones or the translation to your language is not complete, you may contribute to the translation sending your request at email@example.com.
Choose a Currency for the invoice. By default, the currency specified in the profile of the client is used. If the currency is not set in the client's profile, the default currency specified in the CRM settings is used. If necessary, you can select any other currency from the list of the available ones.
If you select a currency that differs from the default currency specified in the CRM settings, the Exchange rate field is also displayed. Set the appropriate conversion rate and click the Save button.
The portal and CRM administrators can change the default currency and set conversion rates for the currencies from the list in the Settings >> Currency settings
section. For more details please refer to this article
Enter a purchase order number (PO Number), if available, and specify your payment Terms. If you wish to specify the general terms for all your future invoices, click the Set default link below the Terms field, enter your terms and click the Save button.