SpringFramewok HttpMediaTypeNotSupportedException: Content type 'text / plain; charset = UTF-8' not supported

I've been trying to find solutions to this error and can not find it.

Error:

  

2018-07-24 16: 44: 50,541 WARN 25695 --- [nio-8080-exec-2]   .w.s.m.s.DefaultHandlerExceptionResolver: Resolved caused caused   by Handler execution:   org.springframework.web.HttpMediaTypeNotSupportedException: Content   type 'text / plain; charset = UTF-8' not supported

Algorithm in tscript that is called after a button click:

uploadKeySize(e) {
    let keySize = parseInt(e.target.value);
    console.log(keySize);
    this.fileService.sendInfoToGenKey(keySize).toPromise()
        .then(
        data => {
          console.log(data);
        });
  }

file service method that is called and that communicates with the back:

sendInfoToGenKey(sizeKey: number) {
        return this.http.put('http://localhost:8080/operation/request-RSA-keys', sizeKey);
    }

Code:

@RequestMapping(value = "/request-RSA-keys", method = RequestMethod.PUT)
public static KeyPair generateRSAKeys(@RequestBody int sizeKey) throws NoSuchAlgorithmException {
    System.out.println(sizeKey);
    return KeyGenerator.generateKey("RSA", sizeKey);
}