Your stream has no picture. The reseller says you must use HDMI port 1. Not 2, not 3, not 4. Only port 1 works. You move the cable. It works. The reseller's service is somehow locked to a specific HDMI port. Your other devices compete for that port.
A British IPTV reseller who requires a specific HDMI port has a bizarre requirement. HDMI ports are identical. There's no technical reason for this. The reseller is either incompetent or using a fake requirement to seem knowledgeable.
The British IPTV services that work on any HDMI port are properly designed. No port restrictions. The reseller who requires port 1 is making up requirements.
The IPTV reseller panel doesn't care about HDMI ports. The reseller's app doesn't either. The reseller is inventing fake troubleshooting steps.
The IPTV reseller UK operators who know what they're doing never mention HDMI ports. The resellers who do are making things up.
Here's a scenario that creates cable management headaches. Your TV has 4 HDMI ports. Port 1 has your soundbar. The reseller says you must use port 1 for IPTV. You have to unplug your soundbar or choose which device gets the "magic" port. You rearrange everything. The IPTV works. Your soundbar is now on port 3. Nothing changed except your inconvenience.
The requirement was fake. Any port would have worked. The reseller wasted your time.
I've tested HDMI port requirements across dozens of resellers. None have legitimate port requirements. Resellers who claim you need a specific port are making up troubleshooting steps.
An honest British IPTV reseller will never mention HDMI ports in troubleshooting. You can test this by reporting a video problem. If they ask about HDMI ports, they're making things up. If they focus on their service, they're professional.
The same principle applies to requiring specific USB ports on streaming devices. Some resellers claim only certain USB ports work. It's fake.
A non fake British IPTV service will give real technical advice. Test by asking for help. If they invent fake requirements, they're incompetent.