currently having the same problem :(
edit: hii so this issue was the same back in feb! i found the dev advice regarding this, they said:
"Could you please double-check the DLC folder name and confirm that it was installed correctly? You can use the image shown on this page as a reference, but the folder should be called "14 Nights With You" and not "14nightswithyou-paid" (or "14nightswithyou-free").
I assume you're getting this error because the file path for the image folder starts with the "14 Nights With You" folder. If it starts with anything else, Ren'Py will ignore it and act like the image can't be found ^^;
If this doesn't resolve your issue, please let me know!!"
i changed the folder named "14nightswithyou-paid" to "14 Nights With You" as well but then it said i didnt have the dlc so i changed it back to the previous name and instead moved the "14 Nights With You" folder inside the "14nightswithyou-paid" folder of the base 14 Days With You game directory.
sorry.. i dont know to explain it better;;