On financial documents, seven is written with the complex form, not 七.
Tips
usage
柒 is the 'capital' numeral for 七 (seven), used on checks, contracts and receipts so the figure can't be altered by adding strokes. The full set runs 壹贰叁肆伍陆柒捌玖拾.
The three-drop water form 氵 sits on the left; the character was borrowed phonetically for 'seven', so the water element is structural rather than meaningful here.