It may happen that you last logged in to the flespi panel a while ago and forgot your credentials. To perform a one-time login:
Go to https://flespi.io/, click the red Login/Register button
Pick the region your account was registered at and click on the email button:
Once you get into the flespi panel via the link, click on the avatar in the top left corner and navigate to the Change password item. Set the new permanent password for your account and save it.