imessage not working via Ethernet connection

For some reason iMessage won’t work on an iPhone via Ethernet connection. All other apps and connections work, but not iMessage. Also, iMessage works fine on iPads via Ethernet, but not iPhones? If you try to send an iMessage via Ethernet on an iPhone, it refuses and tells you to enable WiFi. But on an iPad, the messages go through just fine. Our house has “dead zones” where WiFi and cell don’t work well, so Ethernet is the most reliable option. Unfortunately iMessage won’t work via Ethernet on iPhones for some reason?