Custom Additional Menu missing - GP 2016 Web

I'm trying to add a custom Menu to Purchase Order Entry window. below is dex script for same. 

l_result = Trigger_RegisterForm(anonymous(form POP_PO_Entry), "My Menu", "S", script MyScript);
if l_result <> SY_NOERR then
	warning "Form trigger registration on POP_PO_Entry failed.";
end if;

I can see the menu in GP Windows but the menu is missing in GP web. Am I missing anything ? Isn't it suppose to work the same way for GP Web as well ?

Thanks in advance for help!

Himal