1. three mistakes      -> 422
     A customer id looks like C0047.
     The quantity must be a whole number from 1 to 100.
     A rack looks like A07: one capital letter, two digits.
2. unknown customer    -> 422
     There is no customer C9999.
3. correct form        -> 302 /Bills/Detail/B2954
   the bill page       -> 200
     Bill B2954 created: 4 x Rp 8.000 = Rp 32.000.
4. Pay      50000 -> 302; status queued, balance Rp 32.000; The amount must be from Rp 1 to the balance, Rp 32.000.
5. Pay      20000 -> 302; status queued, balance Rp 12.000; Payment of Rp 20.000 recorded.
6. Advance        -> 302; status finished, balance Rp 12.000; Bill B2954 is now finished.
7. Advance        -> 302; status departed, balance Rp 12.000; Bill B2954 is now departed.
8. Advance        -> 302; status departed, balance Rp 12.000; Bill B2954 has already been collected.
9. no token (forged)   -> 400
