The file I uploaded was a zip file containing the OPK file. So you just need to open/extract the ZIP file and then upload the OPK file to Sub Squared. Winrar, 7zip or the inbuilt zip capabilities in Windows or Macos should work for extracting the ZIP. If you don't get an error when uploading the OPK file to Sub Squared then it'll be a valid OPK format.
If you are still having problems let me know and I'll try to help.
If you are still having problems let me know and I'll try to help.
How do you unpack an opk file --I thought 7zip would be able to do it.