There's only one person and one device able to access one account at a time. If you use several devices to play, you need to close the app on one device and press Reconnect on the device you want to play.
Note that granting access to the account to other people, as well as activities like selling, trading, and gifting are violations of our Terms of Service. These actions could potentially expose your personal and confidential information, putting you at risk of financial fraud. We can't assure the security of any account that has changed ownership. Furthermore, we may apply penalties to any account that has been transferred between players.
If you haven't shared your account with anyone and have noticed unusual activity on your Google/Apple account, contact our Support Team for further assistance.