iPhone 15 pro, problem with external storage device

Have you eliminated there being an issue with the external drive (by connecting it to another iPhone or an iPad if available or a computer or any other device to see if it functions correctly)?

Hi Jo3666,

If your iPhone is not detecting an external device, review Allow USB and other accessories to connect to your iPhone, iPad, or iPod touch as:

• "If the accessory is still not recognized after you unlock your device, disconnect your device from the accessory. Then unlock your device and reconnect the accessory."
• Check your settings as "If you don't connect to accessories regularly, you might need to turn on this setting manually."

If it continues, review Connect external storage devices to iPhone, note:

• " An external storage device must have only a single data partition, and it must be formatted as APFS, APFS (encrypted), macOS Extended (HFS+), exFAT (FAT64), FAT32, or FAT. To change the formatting of a storage device, use a Mac or PC."
• "External hard drives often require an external power source when used with iPhone. If an external hard drive doesn’t supply its own power, and your iPhone has a USB-C connector, you can use a powered USB hub. If your iPhone has a Lightning connector, you can use the Lightning to USB 3 Camera Adapter connected to a USB power adapter."

Take care.

I've just purchased an iPhone 15 pro and SansDisk extreme pro SSD. The SSD will connect to MacBook Pro no issues. However, it does not connect to the iPhone 15. I've changed the USB-C cables, I've tried turning it on and off with the SSD attached too. Nada! I purchased both devices to seamlessly move video files from the phone to the SSD. Not sure what else to try.

After having the same exact issues as OP and the many others on here, I tried Apple brand USB-C to USB Adapter. ($19.99 USD) FIXED SOLVED Hope this helps.