You should first confirm that the card is working by having it read by your computer. I am an avid Samsung user and think it is worth mentioning the Samsung Smart Switch really takes quite a bit of the headache out of swapping phones. Micro SD Card, Xinber High-Speed TF Flash Memory Card with Adapter, Full HD Video V30, FAT32, 667X, U3, C10, Ultra MicroSDXC UHS-I Card for Smartphone/Bluetooth Speaker/Tablet/PC/Camera/Dash Cam (1TB), 512GB 1024GB Micro SD Card Memory Card with Adapter High Speed Class10,U1,A1,TF Card MicroSD (512GB Orange), SAMSUNG: EVO Select 128GB MicroSDXC UHS-I U3 100MB/s Full HD & 4K UHD Memory Card with Adapter (MB-ME128HA), FREE Shipping on orders over $25 shipped by Amazon, Samsung (MB-ME128GA/AM) 128GB 100MB/s (U3) MicroSDXC EVO Select Memory Card with Full-Size Adapter, SanDisk 256GB Ultra microSDXC UHS-I Memory Card with Adapter - 100MB/s, C10, U1, Full HD, A1, Micro SD Card - SDSQUAR-256G-GN6MA, SanDisk 1TB Extreme microSDXC UHS-I Memory Card with Adapter - C10, U3, V30, 4K, A2, Micro SD - SDSQXA1-1T00-GN6MA, Samsung 128GB EVO Plus Class 10 Micro SDXC with Adapter (MB-MC128GA), Samsung Evo Plus Class 10 UHS-I microSDXC U3 with Adapter (128GB MB-MC128GA/APC), SanDisk 128GB Ultra Micro SDXC Memory Card Bundle Works with Samsung Galaxy J7 (2017), J7 (2018), J7 V (2018) Phone UHS-I Class 10 (SDSQUAR-128G-GN6MN) Plus Everything But Stromboli (TM) Card Reader, Samsung 64GB Evo Plus Micro SDXC Memory Card Class 10 (MB-MC64) Works with Samsung Galaxy J7 (2018), J7 Star, J7 V (2018) Phones Bundle with (1) Everything But Stromboli MicroSD/SD Card Reader, Samsung 128GB Evo Plus Micro SDXC Memory Card Class 10 (MB-MC128HA) Works with Samsung Galaxy J7 (2018), J7 Star, J7 V (2018) Phones Bundle with (1) Everything But Stromboli MicroSD/SD Card Reader, 256GB/400GB/512GB/1024GB Micro SD Card Memory Card with Adapter High Speed Class 10 MicroSD Card (512GB Black), TomaDisk Micro SD Card 512GB High Speed Class 10 Memory Micro SD SDXC Card with Adapter, Samsung 64GB MicroSDXC EVO Plus Memory Card w/ Adapter (MB-MC64GA), SAMSUNG 32GB EVO Plus MicroSDHC w/Adapter (2017 Model), Professional Ultra SanDisk 64GB Samsung Galaxy S8 MicroSDXC card with CUSTOM Hi-Speed, Lossless Format! Once you have bought memory cards for your J7 from the above link, you will need to insert MicroSD card on your J7 device. Only 20 left in stock - order soon. How to Install SD Card in Samsung Galaxy J7 Smart Phone. (UHS-1 Class 10 Certified 80MB/s), SanDisk 128GB Ultra Micro SDXC Memory Card Bundle Works with Samsung Galaxy J7 Duo, J7 Refine, J7 Star Cell Phone UHS-I Class 10 (SDSQUAR-128G-GN6MN) Plus Everything But Stromboli (TM) Card Reader, Samsung 128GB Evo Plus Micro SDXC Memory Card Class 10 (MB-MC128HA) Works with Samsung Galaxy J7 (2018), J7 Star, J7 V (2018) Phones Bundle with (1) Everything But Stromboli MicroSD/SD Card Reader, 32GB Memory Card, Marceloant Professional 633 x Class 10 UHS-I U3 Memory Card for Computer Cameras and Camcorders, Memory Card Up to 95MB/s, Yellow/Black (32Gb), 2 Pack of 256mb SD Memory Card, 256 mb Secure Digital Flash Memory Cards Pack of 2 with Memory4You (tm) Microfiber Cleaning Cloth, SAMSUNG 32GB EVO Plus MicroSDHC w/Adapter (2017 Model), Professional Ultra SanDisk 64GB Samsung Galaxy S7 MicroSDXC card with CUSTOM Hi-Speed, Lossless Format! To fix this try cleaning the microSD card slot first using a can of compressed air as sometimes dirt stuck in this port can prevent the phone from reading the card.