Hey there yuriko145,
Thanks for reaching out to the Apple Support Communities.
To get started, what's the wattage of the power adapter that you're using with your MagSafe Duo Charger? We ask because to use both the iPhone and Watch charger at the same time, the MagSafe Duo Charger requires at least a 15W adapter.
This information can be found in the 'Related Article' under the "Get faster wireless charging for iPhone 12, iPhone 13, and iPhone 14 models" section: How to use MagSafe Duo Charger with your iPhone and Apple Watch - Apple Support
All power adapters have different ratings for the amount and rate of power delivery. The MagSafe Duo Charger requires the following ratings to deliver faster wireless charging:
* USB-C connector (USB-A is not supported)
* 9V/2.22A power adapter provides up to 11W of power
* 9V/3A and higher power adapter provides up to 14W of power
* iPhone 12 mini and iPhone 13 mini can get up to 12W for faster wireless charging with at least 9V/2.62A
* Higher wattage adapters at or above 9V/3A will also deliver a maximum of up to 14W peak power to your iPhone
To use both the iPhone and Watch charger at the same time, the MagSafe Duo Charger requires at least 15W (5V/3A or 9V/1.67A), but this will result in slower charging.
If not using one of the recommended power adapter, try testing the issues you're experiencing using a recommended adapter from the list above, and let us know if that's able to help.
Best regards.