I send out invoices recurringly. One of my customers doesn't get them sometimes. Once his IT dept had to make a change. But that worked briefly. Most recent failed.

Good afternoon, @amixamabq. 

Welcome to the Community! 

With the details you gave and the issue only occurring with one customer, I recommend contacting our Customer Support Team. They'll be able to use a screen share to review your account with you. Here's how: 

1. Go to the Help ? icon in the top right-hand corner. 
2. Press the Contact Us button. 
3. Enter your question and click Let's talk. 
4. Scroll down and choose to get a callback. 

It's that easy! 

Keep us updated on how it goes. We're always here to lend a helping hand. Take care!