Not a programmer, but some things I found that may be useful:
Decompiled Android app: http://www.javadecompilers.com/data/22.05.18/5234289d435797051e8dcf5b4d2ba0f8/FlowerCare-5.3.0-APKTurbo.com_source_from_JADX.zip
Mirror: https://mega.nz/#!RRtXUARS!6b3eeNa5XfJvhj6lRa_o_DciShwdZdOMnSvhkGtybYQ
Looks like a key file: https://hastebin.com/ufuneyokaf.java
Some work already done figuring out the JSON request: Xiaomi Mi Plants Monitor Flower
Related Android apps:
https://play.google.com/store/apps/details?id=com.xiaomi.smarthome
https://play.google.com/store/apps/details?id=com.huahuacaocao.flowercare
https://play.google.com/store/apps/details?id=com.chug.northconnectedhome