Hey Siri on iOS 10 does not work for Whatsapp

I am using an iPhone 6s, just updated yesterday to iOS 10 and resolved some iCloud issues I had for awhile. I saw that Hey Siri can be used to send WhatsApp messages now, and tried to use it. Everytime I ask Siri to message my sister to test the function, it keeps saying that I have to continue in the app itself. Even when I open the app and try again using the wording 'Hey Siri Message <my sister's name> using WhatsApp', it keeps repeating that I have to 'continue in the app' and only gives the option 'Open WhatsApp'. I already checked my settings and WhatsApp is allowed for Hey Siri. Is anyone else having this problem, or am I doing it wrong?