Thank you for contacting us and I'm sorry about the issue you are experiencing. An keys mismatch error indicates that you have gone through an account reset and either did not reinstall mSecure 5 and(or) did not remove the Dropbox/iCloud sync files if using those feature.
Please remove the Dropbox syncing file to fix your issues here: Dropbox/Apps/mSecure 5/userid/data.mssb
Each mSecure backup file is encrypted with the login password (mSecure 4 or below) or account password (mSecure 5) used when the backup file was created. In order to restore from a backup file you will need to know it's password. Note that backup files created in Dropbox using mSecure 4 for Android are encrypted with the cloud sync password used to set up Dropbox syncing in those versions.
The reason you needed to remove the files is because you set up Dropbox syncing in mSecure 5 with your account previously. You then reset your account, but did not remove the Dropbox files afterwards. The reason this causes an issue is because mSecure 5, for security, looks to match the account key in your local database with the one stored in the sync file. If the keys do not match, it cannot know if it is a valid file. Your account key is created when you start using mSecure 5 on a device initially and on the first device you sign in to after an account reset as well. Going through an account reset and not reinstalling mSecure 5 and(or) removing the previous sync files will always cause this issue.
I reset my phone and reinstall mSecure 220.127.116.116 on my Samsung Note 8 running Android 8.1. However, I'm unable to restore from Dropbox. It kept saying Sync error: Keys mismatch. What keys is it? I have already signed in to my account successfully. Also, I'm unable to restore from the backup files too even I'm using the correct account password.
Can you please help? This is urgent.