Yes you can, but under certain conditions.

The Belgian Tax Authority has stated that people who benefit from the P2P regime can receive tips from customers only via the platform they use. 

This means that you can receive tips from a customer through the Deliveroo app, but you cannot receive tips directly from customers in cash when riding with the P2P status. 

If you get a tip directly from a customer in cash after delivering an order, all your income earned via the platform Deliveroo will be excluded from the P2P regime, and you may be taxed on your income as a self-employed rider.