PATCH Web Service

//PATCH: Partially update existing data or resources in Salesforce.
	@future(callout=true)
    public static void patchContact() {
        HttpRequest req = new HttpRequest();
        // SourceOrgNamedCredential is your SourceORG Named Credential
        // 003F900001gMifVIAS is the Id of targetORG contact which we are updateing
        req.setEndpoint('callout:SourceOrgNamedCredential/services/apexrest/Contact/003F900001gMifVIAS');
        req.setHeader('Content-Type', 'application/json');
        req.setHeader('Accept', 'application/json');
    
        // Use a map to represent the request body and serialize it
        Map<String, String> requestBodyMap = new Map<String, String>{
            'contactFirstName' => 'Updated Steven',
            'contactLastName' => 'Updated Foster'
        };
        String requestBody = JSON.serialize(requestBodyMap);
        req.setBody(requestBody);
    
        req.setMethod('PATCH');
    
        Http http = new Http();
        HttpResponse response = http.send(req);
    
        // Error handling
        if (response.getStatusCode() == 200) {
            system.debug('Contact updated successfully');
            system.debug('Response body: ' + response.getBody());
        } else {
            system.debug('Error updating contact. Status code: ' + response.getStatusCode());
            system.debug('Response body: ' + response.getBody());
        }
    }