Path params not getting passed properly during http-proxy integration

getting the below error , while passing the path params in http-procy integration in serverless.yml

> user_authenticate:
>     handler: src/subs/index.create_proxy
>     events:
>       - http:
>           path: apps/{application_identifier}/sbs/user/{user_identifier}/authenticate
>           method: get
>           integration: http-proxy # http or http-proxy
>           cors: true
>           request:
>             uri: "${self:provider.environment.Sbs_USER_URI}/{user_identifier}/authenticate" # required
>             method: get # optional, defaults to http.method 
>             RequestParameters: 
>              integration.request.path.user_identifier: method.request.path.user_identifier

Error :
Execution failed due to configuration error: Illegal character in path at index 36: https://api.fastspring.com/accounts/{user_identifier}/authenticate

Kindly help me in resolving the issue .