I've asked the same question on stackoverflow: https://stackoverflow.com/questions/76433285/esp8266-at-mqtt-ssl-certificates-not-working?noredirect=1#comment134776091_76433285 I'm using the ESP8266 (WROOM-02D) for MQTT over WIFI. I'm using AT commands for MQTT. I'm currently using ESP8266-IDF-AT_V2....