Build the Callout Service

public class CurrencyConversionService {
    public Decimal convert(Decimal amountInZar, String targetCurrency) {
        HttpRequest request = new HttpRequest();
        request.setEndpoint(
            'https://api.example.com/convert?from=ZAR&to=' + targetCurrency + '&amount=' + amountInZar
        );
        request.setMethod('GET');

        HttpResponse response = new Http().send(request);

        // ... handling the response comes in the next lessons ...
        return null;
    }
}

1. public class CurrencyConversionService { — the service class.
2. public Decimal convert(Decimal amountInZar, String targetCurrency) { — matching Lesson 1's sketched signature exactly.
3. HttpRequest request = new HttpRequest(); — an empty request.
4. request.setEndpoint( — opens the endpoint call.
5. 'https://api.example.com/convert?from=ZAR&to=' + targetCurrency + '&amount=' + amountInZar — matches Lesson 1's contract's query parameters, in order.
6. ); — closes setEndpoint.
7. request.setMethod('GET'); — matches the contract's GET.
8. (blank line)
9. HttpResponse response = new Http().send(request); — sends it.
10. (blank line)
11. // ... handling the response comes in the next lessons ... — a placeholder, not yet implemented.
12. return null; — a temporary stand-in return value.
13. } — closes the method.
14. } — closes the class.

This directly matches Lesson 1's request contract — GET, the query parameters in the exact order specified, built with Module 36's HttpRequest shape.

public Decimal convert(Decimal amountInZar, String targetCurrency) {
    HttpRequest request = new HttpRequest();
    request.setEndpoint('https://api.example.com/convert?from=ZAR&to=' + targetCurrency + '&amount=' + amountInZar);
    request.setMethod('GET');

    HttpResponse response = new Http().send(request);

    if (response.getStatusCode() == 200) {
        System.debug('Callout succeeded: ' + response.getBody());
    }

    return null; // parsing comes in Lesson 4
}

1. public Decimal convert(Decimal amountInZar, String targetCurrency) { — the method signature.
2. HttpRequest request = new HttpRequest(); — an empty request.
3. request.setEndpoint('https://api.example.com/convert?from=ZAR&to=' + targetCurrency + '&amount=' + amountInZar); — unchanged from the previous section.
4. request.setMethod('GET'); — unchanged.
5. (blank line)
6. HttpResponse response = new Http().send(request); — sends it.
7. (blank line)
8. if (response.getStatusCode() == 200) { — checks whether the callout actually succeeded.
9. System.debug('Callout succeeded: ' + response.getBody()); — confirms the mechanics work before adding real logic.
10. } — closes the if.
11. (blank line)
12. return null; // parsing comes in Lesson 4 — still a placeholder.
13. } — closes the method.

At this stage, the method confirms the callout mechanics work — sending a real request and getting a real 200 response back — before adding parsing (Lesson 4) or error handling (Lesson 5) on top of a foundation that's already confirmed to work.