[ToDo] Backend unify to use JSON for POST and PUT data

[William-An]

TODO: Use JSON

What is this todo related to?

backend

What is the todo?

Use JSON

How urgent is the todo?

Should this be done by... i.e. (as soon as possible, anytime within the current development cycle, anytime within the next development cycle, sometime) note: if it is critically urgent, please add "!important" label

Additional context

Add any other context about the problem here.