There is a new e-commerce in the city. Can you buy a flag for me? I know it's a bit expensive, but please try!
There is a bug when the new credit is computed after buying something. If the quantity of the item is below zero, you can add money to your account! Simply buy -10000000 cows and you're set.
havceCTF{d0nt_lo0k_at_0ur_w3b_d3s1gn_sk1llz_als0_r3m3mb3r_t0_ch3ck_f0r_n3g4t1v3s}