My dashlane app won't sync because it needs a later version on ipad

Hello, this is Xavier from Dashlane's support team. It appears that you are running iOS 8 and I am afraid we have stopped updating the app for this version of the system. It now requires iOS 10.

You may want to try and tap "Settings > General > Software Update" to check whether you can upgrade your system to a newer version of iOS. If not, you should be still able to run an older version of Dashlane (version 4.1.0) and sync your data though. Please get in touch with us here: https://support.dashlane.com/hc/en-us/requests/new so our technical support team can investigate and assist you directly. Thanks!

Which iPad do you have?

See in Settings > General > About > Model

If you have a first gen ipad then you cannot run the latest iOS which is ten. There really is no solution beyond buying a newer device.