What are you using to make the REST Calls? are you trying to do this on the URL or using curl or Postman?
What does your postman call look like?
That isn't a pure rest call.
You need to set up Postman as a PUT remove the method piece and put the appkey into the Headers and the value into the body.
There are some REST tutorial posts that can help you here in the community.
See I'm getting error 405 Method not allowed. Please help me with this.
Attached is a screen grab of a PUT call that works. Here is a guide that covers setting a value using a REST call:
https://developer.thingworx.com/resources/guides/rest-api-how-guide/property-values-rest-api-how
Are you trying to set a value on a Thing named: "Remote1(c6e3ba02c6ef6922)" or "Remote1"
I do not see any body in your PUT call, you must include the property name and value in the body of the PUT