I’m not certain that this is true, unless there’s evidence here/somewhere of Bubble saying the contrary. When migrating, historically, you’ve been charged for all WU in the calendar month (because for some silly reason, WU is synced with the calendar month rather than the app billing cycle) and I haven’t seen anywhere that it’s change.

The email also indicates that regardless of billing cycle, monthly plan apps will migrate on October 1st (perhaps to avoid incurring WU charges for the previous month).

That said, I read just about everything Bubble puts out, so if I don’t understand how a migration is charged then someone that gets that email after 18 months without even logging into the Bubble editor will have no clue!