I'm testing out the Stack Exchange API with a tiny script that fixes a typo.
It's written in PHP and used the implicit client-side OAuth flow to get the access token.
Lessons learned
{"error_id":400,
"error_message":"POST methods expects all parameters to be submitted as a form, not on the query string","error_name":"bad_parameter"}
Do not send JSON but a application/x-www-form-urlencoded
POST request.
The write API is seriously underdocumented as noted in 2013 already: Tell us that POST is required to write
{"error_id":400,
"error_message":"body","error_name":"bad_parameter"}
Even if you just want to change the title, you need to send the body. The body must be markdown, and your filter to fetch the body must be unsafe.
{"error_id":400,
"error_message":"tags","error_name":"bad_parameter"}
You also have to set the tags, even if you only change the title.
{"error_id":403,
"error_message":"Applications must have a registered Stack Apps post to write","error_name":"access_denied"}
This post here exists because of this message. Add the post URL to your stack apps entry.