Samsung Galaxy S9 Plus: How to Insert / Remove SD Card - YouTube
Here is the official spec sheet for the Galaxy S9 and Galaxy S9+ - SamMobile
Amazon.co.jp: Samsung Galaxy S9 Memory Card SanDisk 256GB Ultra Micro SD SDXC UHS-I Class 10 works with S9+, S9 Plus (SDSQUAR-256G-GN6MA) with Everything But Stromboli (TM) Card Reader : Computers
Galaxy S9/S9+: How do I install the memory card ? | Samsung Gulf
Pro Compatible with Samsung Galaxy S9 + / S9 SIM and Micro SD Card Tray : Electronics - Amazon.co.jp