The most common cause for the extra text error is additional “” signs in the json string. Please check the formatting of the jsoncode. You can also try using the fileread function instead of fread and since you are not providing the full path please add a check before fid to make sure that it is valid.
fileName = 'filename.json'; % filename in JSON extension
str = fileread(fileName); % dedicated for reading files as text
data = jsondecode(str); % Using the jsondecode function to parse JSON from string
The following link provides the information for decoding or creating JSON formatted text.
