It could be mainly for 2 reasons:

The "reset your password email" was sent to your spam inbox.

The email address you entered does not exist because it
Contains a typo or a misspelling
You are trying to "Log in" to the Aktiia app using the credentials of the Aktiia website (used only for orders). Those two accounts are independent. Aktiia App will not recognize your website credentials. Make sure you create a new account by clicking “SIGN UP” and not “Log in”