Bin/gpm self-upgrade on Windows (MAMP)

I am trying to upgrade my Grav with bin/gpm self-upgrade but I get an error when it tries to download the zip-file from Github. I am running MAMP on Windows for my local installation.
I user php bin\gpm self-upgrade.

I get the following error message.

[RuntimeException]
  Error while trying to download 'https://github.com/getgrav/grav/releases/download/0.9.
  15/grav-update-v0.9.15.zip'

From what I can read from the Learn page, it should be possible to use bin/gpm on Windows.
Any suggestions?

That URL doesn't actually have a space in it correct? When i copy-paste it, i get a space between the first 0.9. and the 15.

The proper URL is: https://github.com/getgrav/grav/releases/download/0.9.15/grav-update-v0.9.15.zip

And this pasted into a browser, does indeed download the file correctly. If that URL is output properly on your side, then the problem is likely related to MAMP's CLI PHP not being able to reach the SSL based URL. I'll do a little research...

I think thats just a linebreak when I copy and pasted it. I'll check in the morning. Is there any dependencis for this? Other then what default i MAMP?

Also you need to make sure you have php_openssl extension enabled. I've seen this issue coming up before and it was because on windows openssl is not enabled by default.

php_openssl is enabled by default in MAMP from what I can see.

PHP Requirements are here in the docs, and it works fine for MAMP on mac out-of-the-box. As w00fz says, it might be a windows thing. MAMP for windows is still an alpha quality release, and might not be properly configured.