Error:An unhandled exception was caught by the X++ Custom Services controller - Parameter count m...

...ismatch using postman

I am trying to access the API based web service created in Microsoft Dyanamics D365 for Operation and my service is having the single parameter. when i try to pass the parameter it is throwing below error. I am using Oauth2 token when i call service without parameter it is working as expected, but when i call a simple service with parameter i am getting error marked in title. Kindly help.