Hello @LouisLIU.
Please ensure you activate and use your SIM in the UK before travelling abroad.
There is the option to purchase the Roaming Pass if you have an active subscription pack which will allow you to use your allowance as you would in the UK. This is charged at £2.50 per day or £10 for 7 days.
You can find information on Roaming in France HERE.
Katie 🙂
