How to specify a variable in the path prefix of an External HTTP (RFC) connection (in transaction SM59)

Hi There,

Please can someone tell me how to specify a variable in the  path prefix of an External HTTP (RFC) connection in transaction SM59?

For example if my path prefix is /invoke/test/example?input=XYZ; how do I replace "XYZ" with a variable so that I can pass in any value after "=" ?

Thanks,

Brendon