Possible Cause - REST API Keys aren't configured for your Wise-Sync User Account (ConnectWise v2019.3)
A variation of the error in the title - if you're seeing the error below:
Failed to get billing contact for company.
(Company: xxxxx | Error: { "code": "Unauthorized", "message": "Incorrect public/private key" })
And you're using ConnectWise v2019.3 make sure you have REST API keys configured for your Wise-Sync User Account. See FAQ - How to create REST API Keys for a ConnectWise Member for steps to configure.
Possible Cause - no phone number for the contact
ConnectWise is currently returning a NULL value for a phone number, where a contact does not have a phone number selected.
This is normally as a result of no phone number being listed on the contact page.
This issue has been logged with ConnectWise. A work-around has been implemented that will accept the invalid data from ConnectWise (discarding the NULL value) and update Xero with all other contact information.
Please ensure that a Phone Number is selected from the contact numbers in ConnectWise.