I just found something interesting. I'm not sure how much further I'll get, but after receiving the error message about 'Method Not Implemented', I tried re-uploading the .zip without clearing the temp files the installer was asking me to get rid of. It loaded fine, said the extension was installed,...
I have exactly the same problem on a fresh install of Open Cart 220.127.116.11. I've tried different browsers and installed the QuickFix that's been mentioned elsewhere, and still nothing. Were you able to get any assistance?