After click launch button in the course throws an error below and won't load:

(99999) An unknown error occurred. Please try again. If the situation persists, please contact the site administrator. (@001) com.fasterxml.jackson.core.JsonParseException: Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false') at [Source: (String)" 411 Length Required

Error: Length Required

POST requests require a Content-length header.

"; line: 2, column: 2]


What could be done?,