IR codes, how does it work?

I am trying to use the IR codes from the manual section but do not understand it.
It states that the codes all end with 8989 and that you have to change the first 2 digits

…but I got one code example that is the following:
Arylic Remote PowerToggle IR code BF408989

That is a total of 8 digits but your are only giving 6
My question is where do we get digits 3 and 4?

digits 3 and 4 is used to verify the first 1,2, the first 2 bytes adds to 0xFF.
For example, BF408989, 0xBF+0x40=0xFF