The item is not compatible.
'Compatibile' — com-pa-TI-bi-le. Five syllables.
Use for accessories, cables, software, or parts that do not work with your existing equipment. State what you have at home so the assistant can help find the right product.
'Compatibile' is an adjective that does not change for gender but changes for number: 'compatibili' (plural). 'Non è compatibile' is a simple negative copula construction. You may need to specify: 'non è compatibile con il mio iPhone'.
Non si adatta al mio dispositivo.
It doesn't fit my device.
More casual — for physical fit.
Non funziona con il mio sistema.
It doesn't work with my system.
For software or digital products.
Ho bisogno della versione per Android.
I need the Android version.
Specifies what you actually need.
Italian electronics shops (Unieuro, MediaWorld) have staff trained to help with compatibility. Always bring the device or note the exact model name before going to the shop — it speeds things up enormously.