The Leica SL2 features two memory card slots and both slots are compatible with UHS-II (SD/SDHC/SDXC) memory cards. They are also backwards compatible with the slower UHS-I (SD/SDHC/SDXC) cards.
For shooting video at up to 5K 30 p we would recommend an SDXC UHS-II memory card with a V90 video rating.
It's always a good idea to format a new memory card before use. In the Leica SL2's menu's SETUP section, select Format. Then in the submenu select which of the two card slots you want to format and confirm the action.