9 days after purchasing, I received an email from the developer saying that someone was trying to reset the account to its first email address.
They then contacted me to ask if it was me and where I got the account from.
After I explained that it wasn’t me and that I had bought it here, they fully blocked the account because account transfers and sales are against their rules.
So be careful — you could lose your account within a few days, or someone might try to change the password and email address again.