Calling PATCH API method returns 400 error?

[simone_decato216]

I'm trying to call a SAP ARIBA API using the PATCH method within a S4 HANA ABAP system, but I always get the 400 code with an error message stating :"contentTypeIncorrect".
The SAP ARIBA API documentation gives a very clear example in ABAP, where it is clear that it should work.

******

DATA: lo_http_client TYPE REF TO if_http_client.
DATA: response TYPE string.

"create HTTP client by url
"API endpoint for API sandbox 
CALL METHOD cl_http_client=>create_by_url
  EXPORTING
    url                = 'https://sandbox.api.sap.com/ariba/api/approval/v2/sandbox/{approvableType}/{approvableId}'

  IMPORTING
    client             = lo_http_client
  EXCEPTIONS
    argument_not_found = 1
    plugin_not_active  = 2
    internal_error     = 3
    OTHERS             = 4.

IF sy-subrc <> 0.
  "error handling
ENDIF.

"setting request method
lo_http_client->request->set_method('PATCH').

"adding headers
"API Key for API Sandbox
lo_http_client->request->set_header_field( name = 'APIKey' value = 'jZROiOY0vaQrVnAAUGiA6vhGC6SyPPhh' ).
lo_http_client->request->set_header_field( name = 'DataServiceVersion' value = '2.0' ).
lo_http_client->request->set_header_field( name = 'Accept' value = 'application/json' ).
lo_http_client->request->set_header_field( name = 'Content-Type' value = 'application/json' ).


CALL METHOD lo_http_client->request->set_cdata
  EXPORTING
    data = '{\n   "state": "approve",\n   "comment": {\n      "text": "string",\n      "visibleToSupplier": true\n   }\n}'.

CALL METHOD lo_http_client->send
  EXCEPTIONS
    http_communication_failure = 1
    http_invalid_state         = 2
    http_processing_failed     = 3
    http_invalid_timeout       = 4
    OTHERS                     = 5.

IF sy-subrc = 0.
  CALL METHOD lo_http_client->receive
    EXCEPTIONS
      http_communication_failure = 1
      http_invalid_state         = 2
      http_processing_failed     = 3
      OTHERS                     = 5.
ENDIF.

IF sy-subrc <> 0.
  "error handling
ENDIF.

response = lo_http_client->response->get_cdata( ).

WRITE: 'response: ', response.

{ "error": { "code": "contentTypeIncorrect", "message": "Content-Type supported is 'application/json'" } }I tried to use Postam to test the service and I don't get the same error

Have you faced the problem or do you have any suggestions?

Thank you
Simone

[giovanniklein1]

Yes, it is necessary to change the abap code call to a lower level:

l_http_client=>create_by_url(
EXPORTING url = lv_url
IMPORTING client = lo_http
).

lo_http->request->set_method( 'PATCH' ).
lo_http->request->set_header_field( name = '~request_method' value = 'PATCH' ).
lo_http->request->set_header_field( name = 'Content-Type' value = 'application/json' ).
lo_http->request->set_header_field( name = 'APIKey' value = gc_api_key_attach ).
lo_http->request->set_header_field( name = 'Authorization' value = |Bearer { lv_token }| ).

DATA: lv_body_xstr TYPE xstring.

CALL FUNCTION 'SCMS_STRING_TO_XSTRING'
EXPORTING
text = lv_body
mimetype = 'application/json'
IMPORTING
buffer = lv_body_xstr.

" Insert payload directly
CALL METHOD lo_http->request->set_data
EXPORTING
data = lv_body_xstr
offset = 0
length = xstrlen( lv_body_xstr ).

"Send the request
CALL METHOD lo_http->send.
CALL METHOD lo_http->receive.

CALL METHOD lo_http->response->get_status
IMPORTING
code = lv_status.
lv_error_text = lo_http->response->get_cdata( ).

IF lv_status = 200.
ls_log-ariba_status = lv_sap_stat.
ELSE.
ls_log-log_msg = |HTTP { lv_status }: { lv_error_text }|.
ENDIF.