parsing \\xc3\\xb6 from a url

Question

Hi

I'm trying to support an API, it's a remote server pushing data to me. When passing data, reading directly from $_GET['value'] I get strings with this in them: \xc3\xb6

They also needed a very specific url structure, which I've had to use curl to work around. When using curl on the api I get this instead: \xc3\xb6

Is the problem on my side or on his? How can I decode this reliably? Is there a better way than using curl available? (If neccesary I'll recode that part of it to skip curl, I just wanna get it working at this point).

//edit : Note that I'm writing the $_GET['value'] directly to a file to test. And it looks the same.