I believe this is a battery issue. Which should be cheap
I have the same problem. I found i way to turn boot the phone still though. I just have to stick a pin or similar thing in a little space in the back of the phone and hold it there for about 3 seconds and the phone will be booted. To wake the screen i just downloaded an app where i can use the power button to wake it and also downloaded an app where i can use the sensor beside to front camera to wake it.
Or charger port, which is daughter board
Can't seem to find proper guide
ZTE ZMax Pro (Z981) Disassembly
Or it's charging circuit and requires microsoldering. Not for beginners