A business validation error has occurred while processing your request: Business Validation Error: Make sure all your transactions have a sales tax rate before you save.
Hello and welcome to the Community, 
That error seems to be indicating that there’s an issue with the tax rate that’s been supplied. Can you please share a screenshot showing the what’s been selected for the Rate and Tax fields on that Create Invoice (QuickBooks Online) action?
For example:
I’d like to see if there’s anything in the setup there which might be causing that error here. Please remove/hide any private information from the screenshot before sharing (like names, email addresses etc.).
Looking forward to hearing from you! 
Hello. Thank you for the support.
Please see below screenshot.
Hi there
I’m jumping in to see if I can help!
I did some digging into this, and it seems like the “Tax” field requires the Tax ID. You might need to utilize the Lookup table to match the Tax name from the trigger to the “Tax” field in QuickBooks Online step.
You can learn more about Lookup table here:
Hopefully, this helps! 
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