Hello,
I am a professional software engineer with many years' experience. I am a native English speaker and a great communicator. I have also worked with, built and documented many different APIs over the years, meaning that I have the domain experience you need. I am also fluent in multiple languages including C#, PHP and Java and so reading code is not a problem.
I look forward to hearing from you.
Thanks,
Kendrick
PS. my bid is not final since until I know how large your API is, I cannot quote an exact price.