Hi Thomas;
Refer to the below and construct the url
How to prefill fields and skip first screen with webgui? - Wiki - SCN Wiki
there seems to be a required *(asterisk ) before tcode.
it should be case sensitive also. screenfield also in capital case and also space is there after the tcode and parameter and there is no & there.
/sap/bc/gui/sap/its/webgui?~transaction=* /PERSONAS/LAUNCH <screenfieldname>=FLAVOR;DYNP_OKCODE=SHOP&sap-client=015&sap-language=EN
Regards,
Sarbjeet Singh