problem with business logic method argument

hi dear

good time
i write one business logic api service in java
i have a method that contain one argument with string type as String mobileNumber
when i want test my api method,i can not send mobilenumber as json payload: {“mobileNumber”:“09132124778”}
if i increase my method argument to two or more argument,i can send argument as json payload,but with one argument i can not send it as request body and i get error when call api,but it work perfectly in backendless api inspector

what is the problem?

Hi Hamid

Please provide full error description