Coke contains caffeine, which is decomposed in the liver to produce three primary metabolites: paraxanthin (84%), theobromine (12%) and theophylline (4%). Among them, theobromine belongs to "phosphodiesterase inhibitor", which dilates blood vessels and increases urine output by increasing the content of cAMP in vascular smooth muscle cells.
The knowledge about caffeine in the answer comes from: Zhihu: Why can coffee induce diuresis? -Seoul's answer