InvalidAccountType
Example
{
	"code": "InvalidAccountType",
	"target": "Unknown",
	"details": [
		{
			"code": "InvalidAccountType",
			"number": 2105,
			"message": "Account Type of the account is not firm.",
			"description": "The account type of the account -0- is not firm. A FirmAdmin or a FirmUser can only be added to a firm account",
			"faultCode": "Client",
			"helpLink": "http://developer.avalara.com/avatax/errors/InvalidAccountType",
			"severity": "Error"
		}
	]
}
Explanation

For firm accounts, only FirmAdmin or a FirmUser can be added.