When inviting people to an event at a restaurant, such as a birthday party, and you want to communicate that everyone is expected to pay for their own expenses, you can use a polite and clear phrase like:
"Please note that this will be a 'Dutch treat' event, meaning everyone pays for their own meal and drinks."
OR
"We'll be celebrating at [Restaurant Name], and it'll be a 'pay-your-own-way' gathering."
OR
"Just a friendly reminder that this event is 'self-pay,' so everyone will be responsible for their own bills at the restaurant."
Using any of these phrases will let your guests know that they should be prepared to cover their own expenses and avoid any confusion or awkwardness when the bill arrives.