At this stage, you've tried fixing an issue, but failed – you're not quite sure where to go next…
Don't worry, there are plenty of people who have been there, and needed help! A good start is the main documentation, which is available at https://github.com/postcss/postcss/tree/master/docs. If this draws a blank, then Google is a good option; in addition, there are a couple of other options that may help.
If you spend time researching Google and don't find anyone who has had this problem before, then you can try logging a question on Stack Overflow:

The URL is http://stackoverflow.com/questions/tagged/postcss—this lists all of the questions tagged with the name postcss, and is open to anyone to suggest a course of action or hopefully a tip that will get you back in business. If you do find yourself logging an issue, please try where possible to give details of the system you use (Windows, Mac, or Linux), any screenshots or details of the error, and the steps you were taking to arrive at the error.
Taking things a step further, you can also log a development request, or an issue that requires a change to the code—to do this, please browse to the issues log on the GitHub site, at https://github.com/postcss/postcss/issues:

There are a few things to bear in mind:
package.json, just in case—some of the issues that people experience are as a result of (known or unknown) compatibility issues between plugins, or where a certain order must be followed to ensure plugins can be used.For more details, take a look at this blog posting on the CodePen site: https://blog.codepen.io/2015/07/14/postcss-now-supported-on-codepen/.
With these in mind, good luck! PostCSS is fast gaining ground—with some big name companies using it, such as WordPress and Google, it is sure to become very popular. It would be a shame to give up on something if you come across a problem with using a plugin!
Remember, if one plugin doesn't work, then look around—others may well be available that can take their place. It's a dog eat dog world, where those plugins that are not supported are likely to fall by the wayside, leaving those where support is active and problems are resolved efficiently and promptly.