“Flat rate not supported yet” is a message I get after I try to save an invoice. It worked all last year. I have an iPhone 7

Hi there, @gsanteford.

It looks like this error is related to a business validation error when creating an invoice using API. If you're a developer, I recommend reaching out to our Intuit Developer Support Team. This way, they can perform an investigation on why you're getting this message when saving an invoice.

Here's how you can reach out to them:
 

Go to this link help.developer.intuit.com/s/.

Select General Questions and click Ask a Question.

I'm always here to help if you have any other concerns or questions. Just tag my name in the comment section and I'll get back to you as soon as I can.