"Decoder failed to initialize." Your device can't start decoding. Your seller's stream parameters are incompatible with your device's decoder.
Here's a quick technical breakdown: hardware decoders have limits. A British IPTV reseller who tests on multiple devices knows these limits. A seller who only tests on their own device will ship incompatible streams.
In most cases, a good seller's streams work on 95%+ of devices. A bad seller's streams work on 80%. A terrible seller's streams work on 50%.
What actually works is asking: "What devices have you tested your streams on?" A good IPTV reseller UK has a list. A bad seller says "all popular devices" — which means they haven't tested.
Let me give you a real example. A user's British IPTV worked on his phone but not his TV. The seller had never tested on his TV model. The user returned the service.
Most operators find that decoder failures are device-specific. Sellers who don't test broadly will have many failures.