"[MQTT-3.1.2-1] Incorrect protocol name: "MQIsdp""

I’m trying to get the embedded MQTT-broker in HA running. I think it is running, but when i try Android app My MQTT (https://play.google.com/store/apps/details?id=at.tripwire.mqtt.client&hl=nl), it says “something went wrong can’t connect to broker”, and in the HA log i see many entries like “Invalid connection from (client @ip:port” … “[MQTT-3.1.2-1] Incorrect protocol name: “MQIsdp”” …

I have also tried to install MOSQUITTO MQTT on my raspberry Pi, but this runs into a dependency problem with OpenSSL, https://www.raspberrypi.org/forums/viewtopic.php?t=198213 which i haven’t been able to fix.