Synchronisation d'une Appli javacript vers une API

Description en anglais, vous pouvez répondre en français merci !

We have deployed an Android & iOS App that works offline and online.
It syncs data with a server through an API.
Current sync engine is low performance and full of bugs.
We need to rethink it from scratch and develop a fully functionnal version.

The App is developed with Ionic Framework / Angular JS / Cordova.
We have 3 database models (with associations) to sync (bidirectionnal sync)

Please apply only if you are expert in Javascript / SQL
and if you ever have done such work.

Thank you