Overleaf said "I can't write to the file xx"

Question

I need to read/write csv files so I can save the time of manually formating the table in Latex. It seems that Latex/Overleaf support reading/writing file: https://tex.stackexchange.com/questions/2375/file-input-and-output/637361#637361 write and read from a LaTeX temporary file?

But I dont know where the file is located when using Ovealeaf, although the csv file can be downloaded via "Other logs and files". I tried adding the path in front of the file to write/read, then Overleaf said "I can't write to the file xx". Any tips will be much appreciated.