Spam Message from buyer Last night

[engr_mujahid]

Hi I’m a new seller on Fiverr and I need a solution yesterday I got a message from a buyer with this notification “not spam? Unmark it continue the conversation “this was mentioned
I did unmark and got his work. The work was much difficult as he mentioned during the chat but I completed his work. Later on, he said your provided work is wrong and he goes offline now he is not replying I can do extra work to satisfy him but he disappeared. Only 10 hours left to deliver his work
I’m confused about what If I deliver his work and get negative feedback or the second option I can cancel the order.
Is there any solution kindly guide me I’m worried.