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You can let onpage clicks and conversions be called in Preview Mode using an internal preview cookie, which can be set manually set before testing and should be removed afterwards. All tracking requests having with this cookie set are treaded called as called in Preview Mode, so you can just load the landing page to check onpage clicks, or make a test purchase to see the attribution results immediately.
Preview response with cookie looks different because the preview Json object cannot be sent directly in response body, which is always the one pixel image both on clicks and conversions. The preview Json object is transmitted in the custom http header x-preview-response, which can be found in http log of the browser.
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