Apple Pay may have gotten off to a great start, but adoption and usage rates have already begun to fall, a new study has found. Despite strong iPhone sales, not as many people are trying out Apple Pay, and those who have already signed up are starting to use it less frequently.

"As more and more people buy iPhone 6's we are seeing a lower percentage of them adopting or trying Apple Pay," said Jared Schrieber, CEO of InfoScout. "That shouldn't necessarily be a surprise as we move from people who are early adopters and more likely to try things, to later adopters who are not."

Data collected by InfoScout in collaboration with shows that the number of eligible users who tried Apple Pay dropped from 15.1 percent in March to just 13.1 percent in June. The data suggests this could be partly due to a lack of awareness, with the number of people who said that don't know how the system works rising from 31 percent to 34 percent.

But there has also been a drop in Apple Pay use among existing customers, InfoScout found. Those answering yes to the question "did you use Apple Pay on this transaction?" fell from 39.3 percent to 23 percent, and it appears security and reliability concerns might be to blame for that.

The number of people who are choosing not to use Apple Pay for security reasons rose from 15 percent to 19 percent in June, while the number of people avoiding it for fear it might not work properly rose to 4 percent.

But despite these drops, Apple Pay continues to be the number one mobile payments service, and the most successful one to date. The number of users has been growing since the service made its debut in the U.S. last October, and new merchants are adding support all the time.

Apple Pay also made its international debut in the U.K. last month, and it's expected to reach other regions — including Canada, China, South Korea, and Japan — soon.