Using API to get list folder

Hi!

 

I am trying to use Matlab to get the contents of a folder, my code is:

 

     % Generate the custom header
headerFields = {'Authorization', ['Bearer ', dropboxAccessToken]};
headerFields{2,1} = 'Content-Type';
headerFields{2,2} = 'application/json';
headerFields = string(headerFields);

% Set the options for WEBWRITE
opt = weboptions;
opt.MediaType = 'application/json';
opt.CharacterEncoding = 'ISO-8859-1';
opt.RequestMethod = 'post'; 
opt.KeyName='data';
opt.KeyValue='{"path": "" , "recursive":true}'; 
opt.HeaderFields = headerFields;

%Get data
rawData = webread('https://api.dropboxapi.com/2/files/list_folder',opt');

but I am getting "The server returned the status 400 with message "Bad Request" in response to the request".

 

What am I doing wrong?

 

Thank you