Recently purchased an iplay 7t after reading the xda review. This is replacing an LG v400 tablet that I had rooted. I updated the iplay to build T701_V1.20_20191112, enabled developer options, enabled unlock bootloader in developer options, found the corresponding firmware pac, installed magisk and used it to patch boot.img. So far so good.
I entered fastboot, then I attempted to flash the modified boot.img and was told:
target didn't report max-download-size
sending 'boot' (18584 KB)...
OKAY [ 0.593s]
FAILED (remote: Flashing Lock Flag is locked. Please unlock it first!)
finished. total time: 0.608s
I tried various options to unlock the bootloader:
> fastboot getvar unlocked
finished. total time: -0.000s