spring – How to execute post request in java

I woudlike to send files using rest API :

String setTransferFile = "localhost:8080/api/transferFile";

public void callTransferFile(String nameFile) throws Exception {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        nameFile = "readme.txt";
        HttpEntity<String> entity = new HttpEntity<>(nameFile, headers);
        ResponseEntity<String> result = null;
        try {
            result = restTemplate.exchange(setTransferFile , HttpMethod.POST, entity, String.class);
            logger.info("upload done");
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
        }
        assert result != null;
        if (result.getStatusCode() != HttpStatus.OK) throw  new Exception("upload impossible") ;
    }

But I have always the error… when I try it directly with Swagger UI it works :

500 Internal Server Error: ({"timestamp":"2021-01-12T00:44:33.553+00:00","message":"No such file","details":"uri=/api/transferFile"})