push notification์œผ๋กœ ์—…๋ฐ์ดํŠธ๋งˆ๋‹ค ๋ฉ”์„ธ์ง€ ๋ฐœ์†กํ•˜๋ฉด ์œ ์ € retention rate์— ๋„์›€๋˜๋ ค๋‚˜?? ๊ฒฝํ—˜์ƒ ์–ด๋•Œ??