Error Strongloop Mailgun

{
	"error": {
		"name": "ValidationError",
		"status": 422,
		"message": "The `client` instance is not valid. Details: `email` Email already exists (value: \"a@b.com\").",
		"statusCode": 422,
		"details": {
			"context": "client",
			"codes": {
				"email": ["uniqueness"]
			},
			"messages": {
				"email": ["Email already exists"]
			}
		},
		"stack": "ValidationError: The `client` instance is not valid. Details: `email` Email already exists (value: \"a@b.com\").\n    at /Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/dao.js:317:12\n    at ModelConstructor.<anonymous> (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/validations.js:487:13)\n    at ModelConstructor.next (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/hooks.js:75:12)\n    at done (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/validations.js:484:25)\n    at /Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/validations.js:558:7\n    at ModelConstructor.<anonymous> (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/validations.js:357:5)\n    at /Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/dao.js:1561:9\n    at done (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/node_modules/async/lib/async.js:167:19)\n    at /Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/node_modules/async/lib/async.js:40:16\n    at /Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/dao.js:1545:13\n    at doNotify (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/observer.js:93:49)\n    at doNotify (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/observer.js:93:49)\n    at doNotify (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/observer.js:93:49)\n    at doNotify (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/observer.js:93:49)\n    at doNotify (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/observer.js:93:49)\n    at Function.ObserverMixin._notifyBaseObservers (/Users/andi/xworkspace/woow/loopserver/node_modules/loopback-datasource-juggler/lib/observer.js:116:5)"
	}
}