E.g. a cowboy binding :id must have a corresponding Swagger parameter named id.
Current behaviour is that such constraint is not enforced hence cowboy_swagger generates /api-docs/swagger.json for UI accessible at /api-docs with path that may contain bindings with no corresponding parameter, hence causing curly variable template to be sent to server.
Example: trail with cowboy binding called :id and swagger parameter named key causes this Swagger UI...

... that when clicking Try it out! sends to server something like /places/{id} - i.e. with no replaced value:
2017-03-09 13:15:16.503 [info] <0.942.0> PUT /places/%7Bid%7D