To send an invoice cXML, we'll need a third-party app converter. You can visit our QuickBooks App Store and look for an app that integrates with QBO. Also, you can go to the Apps menu in your QBO account and look for an app from there.
Also, I encourage checking our Help articles page to learn some tips and tricks in managing your QBO account. From there, you can read great articles that can guide you through the steps by steps process.
Don't hesitate to drop a comment below if you have other questions. I'm more than happy to help. Take care!