In delaying its IPO by two years, Japanese messaging app company Line Corp. bought time to correct weak financial reporting controls, work on its business plan, bolster staffing — and left billions of dollars on the table as its valuation shriveled.

Line's initial public offering in the next three weeks is set to raise about $1 billion, which given a global drought of such deals could make it the biggest tech listing this year, but skeptical fund managers point to tepid growth in Line's home market and doubts about its prospects for regional expansion. They also question whether its advertising revenue strategy will work.

In seeking to earn more from its major Asian markets of Japan, Thailand, Indonesia and Taiwan, Line will try to generate more revenue from services such as advertising and offer more localized products, its IPO filing said.