By default WireMock Cloud will serve a generic 404 page if an incoming HTTP request is not matched to any stub mapping. Often this is not a problem, but in some instances it is desirable to serve your own response. This can be achieved using the Priority parameter when creating stubs. By creating a stub which has loose (non-specific) matching criteria and a low priority setting, requests will “fall through” to this if they’re not matched to a more specific stub.

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Example

Suppose you want to serve a 403 Unauthorized response with a meaningful response body when a request is not matched rather than the default 404. Additionally you want to serve 200 response when a GET request is made to /examples/12. Start by creating a stub with ANY as the method. Open the Advanced section and change the URL match type to Any URL. Also in the Advanced section set the Priority to 10 (the lowest). In the Response section, set the Status to 403 and the body content to "Sorry, you can't do that". Create a second stub with the method set to GET, the URL to /examples/12 and the response body to "Example 12 body" (keeping the Status as 200). Now if you make a request that matches the specific stub you will see a response with a 200 status and the success message: 
$ curl -v http://example.wiremockapi.cloud/examples/12

> GET /examples/12 HTTP/1.1
> Host: example.wiremockapi.cloud
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Transfer-Encoding: chunked
<
Example 12 body
Whereas if you make a request to a URL with no stub to match you will see the default 403 response. 
$ curl -v http://example.wiremockapi.cloud/examples/12222222

> GET /examples/12222222 HTTP/1.1
> Host: example.wiremockapi.cloud
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 403 Forbidden
< Transfer-Encoding: chunked
<
Sorry, you can't do that