Setup a method to send Aync call to Heroku, add ‘?_HttpMethod=PATCH’ to the path to notify Heroku it’s a patch request

@future(callout=true)
	public static void callApiEndpointAsync(String apiEndpoint, String method, String aPayload){
		HttpRequest req = new HttpRequest();
		List<String> theArgs = new List<String>();
		HttpResponse res = new HttpResponse();
    try {
      if (apiEndpoint != null) {
        req.setTimeout(120000);
				if ('PATCH'.equals(method)){
					apiEndpoint += '?_HttpMethod=PATCH';
					req.setMethod('POST');
				} else {
					req.setMethod(method);
				}

        setAuthHeaderAsync(req);
        req.setEndpoint(herokuUrl + apiEndpoint);
				if (aPayload!=null)
					req.setBody(String.valueOf(aPayload));

				if (Test.isRunningTest() && (mock!=null)) {
					 mock.respond(req);
			 	} else {
					Integer retry = 0;

					while (retry < 2){
						Http http = new Http();
		        res =  http.send(req);
						if (res.getStatusCode() >= 200 && res.getStatusCode() < 300) {
							retry +=2;
						} else if (res.getStatusCode()==503 || res.getStatusCode()==400){
							retry +=1;
							res = http.send(req);
						} else {
							retry +=1;
							theArgs.add('Api');
							theArgs.add(req.getEndpoint());
							theArgs.add(res.getBody());
						}
					}
					throw new Rest_Exception(ResponseCodes_Mgr.getCode('HEROKU_REQUEST_CALLOUT_FAILED', null, theArgs));
				}

      } else {
        System.debug('Service apiEndpoint and payload must not be null');
        throw new Rest_Exception(ResponseCodes_Mgr.getCode('HEROKU_REQUEST_CALLOUT_FAILED'));
      }
    } catch (Exception ex) {
			theArgs.add('Api');
			theArgs.add(req.getEndpoint());
			theArgs.add(res.getBody());
			throw new Rest_Exception(ResponseCodes_Mgr.getCode('HEROKU_REQUEST_CALLOUT_FAILED', ex, theArgs));
			
    }
}

Spring controller checks the RequestParam _HttpMethod to see if it’s a POST or PATCH request

@RequestMapping(value = "/customer", method = RequestMethod.POST, produces = "application/json")
@ResponseBody
@ApiOperation(value = "Creates new payment customer")
@ApiResponses(value = {@ApiResponse(code = 200, message = "Creates new payment customer")})
public String createCustomer(@RequestBody PaymentCustomerWrapper paymentCustomerWrapper, @RequestParam(value="_HttpMethod", defaultValue="POST")  String httpMethod)
        throws IOException, URISyntaxException {
     if (httpMethod!=null && "PATCH".equals(httpMethod)){
         itsLogger.debug("update payment customer {}", paymentCustomerWrapper.toString());
         return paymentService.updatePaymentCustomer(paymentCustomerWrapper).toJson();
    } else {
         itsLogger.debug("create payment customer {}", paymentCustomerWrapper.toString());
         return paymentService.createChargeBeeCustomer(paymentCustomerWrapper).toJson();
    }
}