Validation for TAX Type via BUS7 transaction

Hi ALL,

I'm trying to implement a Tax Type validation with BUS7 transaction using the event BUTX_BUPA_EVENT_DSAVB or the event BUTX_BUPA_EVENT_DCHCK.

I changed the FM BUTX_BUPA_EVENT_DSAVB by the ZBUTX_BUPA_EVENT_DSAVB (identically copied), I run the BP Transaction in a Debug Mode.  I m not able to get values in the globals parameters using my own Z function modules, for example for GT_BPTAX. All memory fields like partner, taxtype introduced or from master data are lost with my Z FM. With the Standard FM BUTX_BUPA_EVENT_DSAVB the fields have values.

What else do I need to implement or what's wrong with the function?

Very Thanks ! Yenia