Hi dear, I'm new to the freelancer platform but got 3 years of professional hybrid app development.
from Ur project detail, I found that I should build a service that store data in SQLight when the user is offline ;and when user got online the service reads the un-synced data and post it to the server so they could be saved on MySQL database.
I would be pleased if you share more details, data-model and other relevant details of your application.
best regards.