ESP8266 uses D1 (5) and D2 (4), ESP32 uses 21 and 22. Both provide defines for SDA and SCL pin numbers though
Received signals are published to the subjectRF2toMQTT topic (/RF2toMQTT). However, echos of mqtt messages are published to the topic subjectGTWRF2toMQTT (/433toMQTT). That seems quite inconsistent.