You have to provide some more information.
In the web UI it is possible to add attributes to the devices by pressing "+". Then you have to press the Attributes button and add a "Name" and "Value". Is the a unique "Name" for Fuel Level which has the PID code 012F? Is the as list of names which are possible to use?
You can rename existing attributes, not add new ones.
it depends on what device you use.
if the device has more values to send to server then you have to add in the protocol.
It will show all the values for the device accordingly.
attributes are to be used programmatically as a add on values
If I want to add a new attribute to the web UI like Fuel Level (012F) what name and value should I add?