This is my test program:

REPORT ztest_bc.
DATA: strreturn TYPE string.

CALL FUNCTION ‘Z_TEST_BC’ DESTINATION ‘SAPBC’
IMPORTING
OUTPUT = strreturn.

WRITE: / 'Return value: ', strreturn.

Z_TEST_BC call a sap bc service that it has a output value OUTPUT.
When I run this program strreturn variable is always not initial.
Why? Is there a solution? how can I make?

thanks