Error in call to API function "files/list_folder": request body: could not decode input as JSON

The /2/files/list_folder endpoint is an "RPC"-style endpoint, meaning it expects the parameters in the request body (not in a request header). 

Please move your parameters to the request body instead of the "Dropbox-API-Arg" header and try again. (The "Dropbox-API-Arg" header is only used for content-upload and content-download -style endpoints.)

Good morning. 

I go right with this call for about 1 year:

  request = String("POST /2/files/list_folder HTTP/1.1") + "\r\n"
                + "Host: api.dropboxapi.com" + "\r\n"
                + "User-Agent: ESP8266/Arduino_blabla"\r\n"
                + "Authorization: Bearer MYTOKENxxxxx\r\n"
                + "Accept: */*" + "\r\n"
                + "Content-Type: application/json; charset=utf-8" + "\r\n"
                + "Content-Length: " + request_data.length() + "\r\n\r\n"
                + request_data
                ;

request_data = "{\"path\":\"" + MYPATH+ "\"}";

Hi deebee_it,

You haven't mentioned what is the exact "MYPATH".

First: Are you sure the path, you are referring to, exists?

Second: You are relying on utf-8 encoding. Take in mind that Dropbox interpret all JSON input as a ASCII string, the encoding set is ignored! If you are using some simbol(s) outside ASCII set, make sure they are JSON-encoded (\uXXXX, where XXXX is hexdecimal unicode code point).

PS: By the way, you have put in your expression too many, meaningless string additions. Better do some of them join to each other (for example: "Host: api.dropboxapi.com" + "\r\n" could become "Host: api.dropboxapi.com\r\n") and remove the pluses between literals string on different lines (they gonna concatente to each other at compile time). Use pluses only where needed. 😉 In such a way lot of resources gonna be saved and the application speeds up.

deebee_it Based on the output you shared, it seems like the Dropbox servers weren't able to recognize your HTTP request as a valid API call. As Здравко said, it may be helpful to know what your 'MYPATH' value is. Can you print out the entire HTTP request (redacting the access token) so we can see what may not be formatted correctly?

Here is:

POST /2/files/list_folder HTTP/1.1
Host: api.dropboxapi.com
User-Agent: ESP8266-Arduino_blabla
Authorization: Bearer xxxxx
Content-Type: application/json; charset=utf-8
Content-Length: 33

{"path":"/glucose/202011/10/09/"}

Seems http format is acceptable, but what about path existence? For example, you can check the root folder list results on Dropbox API Explorer with empty path and the same access token used here. Does the "glucose" folder appear in the result? 🤔 If Yes, continue the check recursively.

The path exists: I looked directly in my account and I access it with no problem using a js web page!

I tried editing the token in my Arduino call, using a random dummy token... And the error is the same: 4xx... not found...

I thought that the error should be different, or not? :|

Here is the request header of the js web page (that works well OK):

POST /2/files/list_folder HTTP/2
Host: api.dropboxapi.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0
Accept: */*
Accept-Language: it-IT,it;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate, br
Authorization: Bearer xxxxxxxx
Content-Type: application/json
Content-Length: 33
Origin: https://xxxx
Connection: keep-alive
Referer: https://xxxx
TE: Trailers

And the request:

{"path":"/glucose/202011/10/09/"}

Did you check what I have advised above or not? Notice different token could have different access on same account!

Yes, with "Dropbox API Explorer • list_folder" and the *same* token and same path, the call is right.