You should rename the file on the server to remove the .txt extension. You can do this through the command line using the following command:
sudo mv www_highfivestore_in.key.txt www_highfivestore_in.key
It should also be possible to rename the file using Filezilla, by rightclicking on the file and then choose rename.
It's not mandatory, you can rename them as long as you also change the names in the Apache configuration file.
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