Salesforce Multipart/Form-data

ABCService

public class ABCService {
    
    @future(callout=true)
    public static void addJobApplicationFuture() {
        addJobApplication();
    }
    
    public static void addJobApplication() {        
        // Instantiate a new HTTP request
        HttpRequest req = new HttpRequest();
        
        // Set method and endpoint
        req.setEndpoint('https://requestb.in/18so08t1');
        req.setMethod('POST');
        
        // Set body
        String boundary = '----------------------------' + String.valueOf(DateTime.now().getTime());
        String body = '--' + boundary + '\r\n';
        body += 'Content-Disposition: form-data; name="api_access_token"\r\n\n';
        body += 'theaccesstoken\r\n';
        body += '--' + boundary + '\r\n';
        body += 'Content-Disposition: form-data; name="api_version"\r\n\n';
        body += '1\r\n';
        body += '--' + boundary + '\r\n';
        body += 'Content-Disposition: form-data; name="jobapplication"\r\n\n';
        body += createJobAppJSONString() + '\r\n';
        body += '--' + boundary + '--';
        req.setBody(body);
        
        // Set headers
        req.setHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);
        req.setHeader('Content-Length', String.valueof(body.length()));
        
        system.debug('req: ' + req);
        system.debug('req.header.contenttype: ' + req.getHeader('Content-Type'));
        system.debug('req.header.contentlength: ' + req.getHeader('Content-Length'));
        system.debug('req.body: ' + req.getBody());
        
        // Send HTTP request and get HTTP response
        Http http = new Http();
        HttpResponse res = http.send(req);
        system.debug('res: ' + res.getBody());
    }
    
    private static String createJobAppJSONString() {
        JSONGenerator gen = JSON.createGenerator(true);
        gen.writeStartObject();
        gen.writeStringField('channel', 'website');
        gen.writeStringField('firstname', 'jef');
        gen.writeStringField('lastname', 'klaas');
        gen.writeStringField('timestamp', DateTime.now().format('dd/mm/yyyy hh:mm'));
        gen.writeStringField('office_id', '2');
        gen.writeEndObject();
        return gen.getAsString().remove('\r').remove('\n');
    }
}

For me works using just one break line. In the body:

// rest of the code
String boundary = '----------------------------' + String.valueOf(DateTime.now().getTime());
String body = '--' + boundary + '\r\n';
body += 'Content-Disposition: form-data; name="<Key1>"\r\n';
body += 'value1\r\n';
body += '--' + boundary + '\r\n';
body += 'Content-Disposition: form-data; name="<Key2>"\r\n';
body += 'value2\r\n';
// rest of the code```

I am getting the following error when sending a request:
Unexpected end of stream. The content may have already been read by another component.
Please Help!!!!
@viviramji @jovabe