Invalid mime type "File": does not contain '/'

I'm trying to make a post with form data, containing only a file, but when I test the endpoint with Postman I get this error message:

Invalid mime type "File": does not contain '/'

Here is the server side (Spring Webflux). Endpoint:

@PostMapping(value ="/newUpload", consumes = MediaType.MULTIPART_FORM_DATA_VALUE, produces = MediaType.APPLICATION_NDJSON_VALUE)
@ResponseStatus(value = HttpStatus.OK)
public Mono<List<String>> upload (@RequestPart("file") FilePart filePartMono){

    return exampleRepository.getLines(filePartMono).collectList();
}

Service:

@Override
public Flux<String> getLines (FilePart filePartMono){
    return filePartMono.content()
            .map(dataBuffer -> {
                byte[] bytes = new byte[dataBuffer.readableByteCount()];
                dataBuffer.read(bytes);
                DataBufferUtils.release(dataBuffer);
                return new String(bytes, StandardCharsets.UTF_8);
            })
            .map(this::processAndGetLinesAsList)
            .flatMapIterable(Function.identity());
}

private List<String> processAndGetLinesAsList (String string){
    Supplier<Stream<String>> streamSupplier = string::lines;
    var isFileOk = streamSupplier.get().allMatch(line ->
            line.matches(MultipartFileUploadUtils.REGEX_RULES));
    return isFileOk ? streamSupplier.get()
            .filter(s -> !s.isBlank())
            .collect(Collectors.toList()) : new ArrayList<>();
}

In postman I have in form-data the required file and the default headers:

Does anyone have any idea why the problem mentioned at the beginning may be happening?