"code": "NexusDateMismatch",
	"target": "Unknown",
	"details": [
			"code": "NexusDateMismatch",
			"number": 157,
			"message": "Nexus not available on dates specified.",
			"description": "The Nexus for Country: -0-, Region: -1-, JurisCode: -2-, JurisTypeId: -3-, JurisName: -4-, ShortName: -5-, SignatureCode: -6-, StateAssignedNo: -7-, NexusTaxTypeGroup: -8- was only valid from -9- to {10}.",
			"faultCode": "Client",
			"helpLink": "",
			"severity": "Error"

This indicates that you declared nexus on a date when that nexus was not available. When you declare that your company has nexus in a particular jurisdiction, AvaTax checks to make sure that nexus was in existence on the dates you specified.

Because tax authorities create and change their tax rules periodically, some locations are only available for nexus declarations on some dates.