Can I send a payment information request along with the invoice, or should these be sent separately?

When sending an invoice, you can either require your customers to save their card on file or offer them the option to do so. This way, when they make a payment, a payment profile is automatically created in the system, eliminating the need to send a separate Payment Info Request.

To enforce this setting for all invoices/customers, go to "Settings >> Customer Portal Settings", configure as shown below, and save your changes.

If you are not using batch invoice sending, you can handle this on a case-by-case basis when sending invoices. You can override the default setting in your Customer Portal by using the checkbox below when emailing an invoice. Even if this option is turned off, the customer will still have the option to save their card.