json2msgpack -i config.json -o data/config.mp
config.mpfile into an empty folder. Anything in the folder will be uploaded to the SPIFFS partition on the Amp. In my case, I've saved it to a folder called data. Use
mkspiffsto create the SPIFFS partition from the data folder.
mkspiffs -c data -s 61440 spiffs.bin
esptool.py --port COM7 write_flash 0x251000 spiffs.bin