File upload is done by API, normally the HTTP response is in JSON format.If the error says:
SyntaxError: Unexpected token < in JSON at position 0That means the HTTP response starts with “<”, which is probably error message in HTML (not JSON data starting with “{”), which cannot be parsed as JSON and hence syntax error.So there must be error message in F12 → Network, you need to find the request to the API (action=jupload), and click it to view the HTTP response. See https://discourse.hkvstore.com/t/uploading-image-error/1904/1 for more information how to check the HTTP response correctly.