Using base64.h didn't work for me. The recent ESP Arduino code has a base64 with different function signatures which i couldn't stop conflicting, so i had to rename the adamvr one to gBase64 like you had - in the properties file and rename the .h and .cpp file names, and also in the base64.cpp change include for avr/pgmspace.h to just pgmspace.h. (Doesn't seem ideal so will look for a better way, maybe use the ESP/Arduino base64 functions?). Anyway, now:
WiFi connect to: BTHub5-72W5
WiFi connected. local IP address: 192.168.1.119
Wlan Connected
Connecting to UDP
Connection successful
MAC: 18:fe:34:9b:1d:e0:
SX1276 detected, starting.
Gateway ID: 18FE34FFFF9B1DE0, Listening at SF7 on 867.70 Mhz.
Woohoo!