At the final step of claiming your Per Diem sum, you're asked to select the meals you need to deduct. Here's an overview of meals you should select here.
Meals to deduct
Any meal that is paid for with the company's money and that is a business expense should be deducted. There are three common groups:
Meals included in your accommodation
The obvious one here would be breakfast provided by your hotel. But also if there's any other meals included in the price of your accommodation, you need to select them here.
Meals included in your ticket
This can be a lunch included in your conference ticket, or a airplane meal included in your flight ticket's price.
Meals you pay for you and your business partners
These expenses are generally referred to as representation expenses. Most likely you'll pay for them with your Pleo card. Since this is a business expense and it's paid for with company funds through your Pleo card, these meals need to be selected and result in a 20% (breakfast) or 40% (lunch/dinner) deduction of that day's per diem rate.