The Daily capping option is just above the Security Section.
Select the amount that you think is convenient based on your business needs.
Save your settings.
Please be aware that these caps are reset according to the account timezone configuration.
Be also aware that clicks and conversions are asynchronous, this means that between the click and the conversion time there is variable amount of time. Once the cap has been reached, the clicks created from that moment on are automatically paused so no conversions can be triggered anymore. But the clicks that happened before pausing the campaign are still able to convert normally, this is why in some cases, conversions can occasionally arrive to a paused offer.