A similar thing just happened to me. Made a reservation, got the email with the correct price as I reserved. But then checking again online, or at the app and the same reservation has increased by about 10%. I don't think this is related to a limitation of the app because the same higher price is shown online. Never seen something like that, that the reservation at the website shows a different price than the email. Note that it is the very same reservation that suddenly and alone changed price.

I will check with support. I'm not sure it is a good idea to rely on the email alone.