Tried with a new custom entity and the standard entity contact. Both do not work.
Screenshot from the custom entity:

Text output from the custom entity:
Eingaben
The database
default
The entity
MyContact
Record id
5637144576
Name
n1
Name2
b2
Ausgaben
Überschriften
{
"Pragma": "no-cache",
"x-dynint-corrid": "fcfd8b7a-d465-4f45-a1fb-6e625464edfb",
"x-dynint-userid": "09426fa9-dea9-42d8-a6cd-f62d2ce9f7fe",
"x-dynint-tenantid": "f761f78c-7d49-4d1b-b0ec-751b47c38741",
"x-dynint-namespaceid": "default",
"x-dynint-environmentid": "Default-f761f78c-7d49-4d1b-b0ec-751b47c38741",
"x-ms-client-request-id": "8802f7e2-6c87-40e4-a652-84326c7183b4",
"x-ms-correlation-request-id": "fcfd8b7a-d465-4f45-a1fb-6e625464edfb",
"x-dynint-service": "Connector",
"x-dynint-location": "West Europe",
"Strict-Transport-Security": "max-age=15724800; includeSubDomains",
"X-Content-Type-Options": "nosniff",
"Cache-Control": "no-cache",
"Date": "Fri, 04 Nov 2016 08:19:42 GMT",
"Server": "Microsoft-IIS/8.0,Microsoft-HTTPAPI/2.0",
"X-AspNet-Version": "4.0.30319",
"X-Powered-By": "ASP.NET",
"Content-Length": "116",
"Content-Type": "application/json; charset=utf-8",
"Expires": "-1"
}
Text
{
"status": 400,
"message": "No resources were found when selecting for update.",
"source": "rts-connector.powerapps.com"
}
Text output from the contact entity:
Eingaben
The database
default
The entity
Contact
Record id
5637144615
Full name
der tester
Party type
Organization
Source
Default
Is email contact allowed
true
Is phone contact allowed
false
Status
Active
Ausgaben
Überschriften
{
"Pragma": "no-cache",
"x-dynint-corrid": "b5b672cf-e810-4ac7-81c2-95b854526402",
"x-dynint-userid": "09426fa9-dea9-42d8-a6cd-f62d2ce9f7fe",
"x-dynint-tenantid": "f761f78c-7d49-4d1b-b0ec-751b47c38741",
"x-dynint-namespaceid": "default",
"x-dynint-environmentid": "Default-f761f78c-7d49-4d1b-b0ec-751b47c38741",
"x-ms-client-request-id": "78836be6-e678-4f1c-98b8-4b41ca8021fb",
"x-ms-correlation-request-id": "b5b672cf-e810-4ac7-81c2-95b854526402",
"x-dynint-service": "Connector",
"x-dynint-location": "West Europe",
"Strict-Transport-Security": "max-age=15724800; includeSubDomains",
"X-Content-Type-Options": "nosniff",
"Cache-Control": "no-cache",
"Date": "Fri, 04 Nov 2016 08:27:50 GMT",
"Server": "Microsoft-IIS/8.0,Microsoft-HTTPAPI/2.0",
"X-AspNet-Version": "4.0.30319",
"X-Powered-By": "ASP.NET",
"Content-Length": "116",
"Content-Type": "application/json; charset=utf-8",
"Expires": "-1"
}
Text
{
"status": 400,
"message": "No resources were found when selecting for update.",
"source": "rts-connector.powerapps.com"
}