What if seller created two milestone one for design and one for backend

[marronpic]

Seller created milestone one for front design and one for backend process

in case seller completed design part and deliver first milestone and i accept it but he failed to delivery backend code or part in 2nd milestone 

then what will happen fiverr will give amount to seller and return me half amount of 2nd milestone or full amount because project was not completed ?

 

Please help me to understand milestone process :)

[imagination7413]

Numbers 4, 6, and 7: https://www.fiverr.com/support/articles/360010560178-Working-with-Milestones