ZTE ZMAX - Manual (Page 32)

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WARNING! If you interrupt the encryption process, you will lose data.
7. Touch
Encrypt phone.
8. Enter your lock screen PIN or password and touch Next.
9. Touch Encrypt phone again.
The encryption process starts and displays its progress. Encryption can
take an hour or more, during which time your phone may restart several
times.
When encryption is completed, you're prompted to enter your PIN or
password.
Subsequently, you must enter your PIN or password each time you power
on your phone, to decrypt it.