it said the max i could send was 4 million, so i tried to pay myself 4 million and then it told me the real total i could send was 3,989,ABC and then it filled the bar with "3,989,ABC-.05" for example

Welsh Treasury 20,000,000
Max Payment of 5,000,000
Sent Payment of 5,000,000
_______________________
Welsh Treasury 15,000,000
Max Payment of 4,000,000
Tried to Send Payment of 4,000,000 because its the listed max
Error: Max Payment of 3,989,111
Automatically inputs the number above (3,989,111) but subtracts .5 from it, 3,989,110.5
Tried to Send Payment of 3,989,110.5 because it was suggested by game
Invalid Amount to Send but payment of 3989110 works

probably just a typo in the subtraction code giving the weird decimal

Might be because of the tax?

It's a rounding issue. We issued a fix. Probably it is gone now.