UnknownNexusError
Example
{
	"code": "UnknownNexusError",
	"target": "Unknown",
	"details": [
		{
			"code": "UnknownNexusError",
			"number": 145,
			"message": "Unknown nexus: Country: -0-, Region: -1-, JurisCode: -2-, JurisTypeId: -3-, JurisName: -4-, ShortName: -5-, SignatureCode: -6-, StateAssignedNo: -7-, NexusTaxTypeGroup: -8-.",
			"description": "For a list of defined nexus, please use /api/v2/definitions/nexus",
			"faultCode": "Client",
			"helpLink": "http://developer.avalara.com/avatax/errors/UnknownNexusError",
			"severity": "Error"
		}
	]
}
Explanation

This indicates that you attempted to declare nexus in a jurisdiction that is not recognized by AvaTax. For a full list of recognized jurisdictions, please call the endpoint GET /api/v2/definitions/nexus.