Let's make sure you can send invoices to your customer, jay12471.
Yes, you're right. An upgrade is needed to keep the updates compatible with the software. Since QuickBooks Pro 2013 is already unsupported, you'll have to upgrade to a newer version. To do so, you can follow the steps below:
When you’re ready, select Upgrade Now.
Select Keep old version on my computer if you want to keep your current QuickBooks. Then select Let’s go. QuickBooks downloads, install, and activates the new version for you. It updates your company file(s).
When the upgrade is done, select Open QuickBooks.
Also, as services for an older version of QuickBooks Desktop are scheduled to be discontinued, we usually notify you in advance. To know more about this, I've added this article for more information: QuickBooks Desktop Service Discontinuation Policy.