A combination of in-app purchases and website retail payments is projected to drive annual spend via Apple Pay and Android Pay to $8 billion in 2018, up from $540 million this year, according to a study from Juniper Research.

The new study, "Mobile & Online Remote Payments for Digital & Physical Goods: Opportunities & Forecasts 2016–2021," found that the integration of OS-Pay into apps will prove to be a "no brainer" for developers looking to reduce buyer barriers where password entry on smartphones remains cumbersome, according to a press release about the report.

Staples, for example, has already reported that over 30 percent of its iOS app users make in-app purchases through Apple Pay. Meanwhile, despite the continued contraction of the consumer tablet market, more than 85 percent of remote goods payments are forecast to be made using mobile devices in 2021.

"It is clear that even in markets where PCs and laptops have a high installed base that the smartphone is playing an increasingly important role where remote goods purchases are concerned," said Steffen Sorrell, the research author for the report. "For merchants, this means that the buyer experience must be made as frictionless as possible from product search and discovery to purchase."