I doubt it has anything to do with internet connection because this is the only package that gives out an error and it has been so for a week or so now.
Empty the Pamac build directory via Pamac > Preferences > Third Party > Build Directory > Clean & then try building the package again. You currently have a partially downloaded file in the build directory that cannot be resumed by Pamac, so the best thing to do is empty the build directory & have Pamac download the file again. It may not have been able to resume the download if the original file on the server has changed since the partial file was downloaded.
Wrong approach - don’t even try to do that. Not necessary and you will likely mess up your system in short order.
The AUR helpers handle that.
You could try using a different one (yay, for example).