integration test spring restTemplate (POST --> pass List

I want to test method of receiving a list of objects, according to list of given strings. My original method:

@RequestMapping(value = "/fil/", method = RequestMethod.POST)
@ResponseStatus(value = HttpStatus.OK)
public ResponseEntity<List<Tag>> findAllByCpe(@RequestBody Fil fil) {

    return ResponseEntity.ok(tagRepository.findAllBy(fil));
}

Query (tagRepository):

 @Query("SELECT t FROM Tag t WHERE (t.cpe IS NULL OR t.cpe IN (:#{#fil.cpes}))")
    List<Tag> findAllBy(@Param("fil") Fil fil);

Fil (Class holding a list of strings I want to search by)

@Getter
@Setter
@AllArgsConstructor
public class Fil {

    public Fil() {

    }

    @NotNull
    private List<String> cpes;

}

I wrote an integration test:

@Test
public void FindTagGivenListOfCpes() {
    //GIVEN
    List<String> cpes = new ArrayList<>();
    cpes .add("CPE111");
    cpes .add("CPE222");
    cpes .add("CPE333");

    List<Tag> tagList = (List<Tag>) tagTestBuilder
        .saved()
        .itemList()
        .build();

    //WHEN
    ResponseEntity<Tag[]> response = restTemplate.postForEntity(TagsResourceConstants.PATH + "/fil/", tagList.get(0).getCpe(), Tag[].class);


    //THEN
    assertEquals(HttpStatus.OK.value(), response.getStatusCodeValue());
}

I've created an arrayList of strings - Cpes, than I created and save a List of three tags (with exact given Cpes "Cpe111", ...) and I used restTemplate to check if what I search by (cpe) wil give me back the tags with matching cpe (Every tag has one cpe (same as given) already given when I use .itemList method). I have no idea what is missing? I get 415 error :/ I have no idea where to go with that. Basically I just want to test if the objects containg cpes will be found by theirs cpes given under given endpoint.