Hello Tim Chang,
Your question is the same as mine and i have solved this query using the Custom BSP / WebDynpro Application .
I have delivered display sales order using custom application in on-premise system and used that page URL in the HTML mashup and its working well.
I am also trying for display sales order using SICF Service and we can call VA03 but the parameter not pass correctly i have call VA03 from HTML mashup but the VBAK-VBELN and OK_CODE is not pass properly.
Once i solve this query i will update you on same post and also i will send direct msg to you.
Please refer the below screen for same i have done the requirement display Sales Order based on AcccountID and when select Sales Order the VA03 Screen call
I hope this information useful for you .
Many Thanks ,
Mithun