BASE64 requests work only with the POST method.
The reason for this is that a URL is limited in length, and thus can not accept long base64 strings like base64Image=data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAD4AAAAW…
This is also mentioned in the ocr api docs:
The important limitation of the GET api endpoint is it only allows image and PDF submissions via the URL method, as only HTTP POST requests can supply additional data to the server in the message body. GET requests include all required data in the URL. So by design, a GET api cannot support file uploads (file parameter) or BASE64 strings (base64image ).