I'm curious why you want to use HTTP instead of MQTT? One of the design goals of MQTT is bi-directional communication.
By using MQTT, you could have a unique topic per device, that only the device itself is authorized to subscribe to. Then the cloud service can publish a message to the device-specific topic to send a message to that device.
I use a combination of Belkin/Wemo and other devices that are inexpensive and have had the same issues. My solution was to flash them with Tasmota: https://tasmota.github.io/docs/.
This fixed my issue with them being unresponsive but of course, I broke the vendor cloud connection.
My solution was to use homeassistant: https://www.home-assistant.io/ to manage ...