1. Turn data off. This will disable background app refresh too.
2. Insert LFM SIM. You should receive a notification like this. If you don't, send a text to 22213 with message contents of BAL. You'll receive a response with your balance.
3. Subscribe to a data pack: instructions here.
4. Change your APN per this page.
5. Turn data back on.
6. If you're in the EU, but not in France, make sure you have an EU data pack AND roaming on.
Get LFM SIMs from VeloNomad here.