Transacton format for signature is different between wp and reality.

[DronMDF]

This is a line from wp...
12345678abcdef 003a 2017-07-19T21:24:51Z ffffffff9c0ccccd Ui0wpLu7 98bb82c81735c4ee For services

Real transaction string (for signature calculations) look like this:
17737fee5b825835 1195 2018-08-23T17:45:22Z -536870912 paDRj2g1 62e329426a673e68 Hosting bonus for 138.68.95.144 4096 11

1. Transaction id should be int, not hex.
2. amount should be int, not hex.

[0crat]

@yegor256/z please, pay attention to this issue

[0crat]

@DronMDF/z this project will fix the problem faster if you donate a few dollars to it; just click here and pay via Stripe, it's very fast, convenient and appreciated; thanks a lot!