It’s been 23 years since California became the first state to legalize medical marijuana, and five years since Colorado and Washington became the first to make recreational pot legal.

There’s still a big problem.

Cash. A lot of it. Cash isn’t just king in cannabis, it’s almost all there is.

“It’s a huge issue,” said Bob Groesbeck, co-CEO of Planet 13, a massive marijuana superstore in Las Vegas doing over $5 million a month in sales. Groesbeck has managed to bring in some credit card capabilities to his store, without revealing details. “I’d still say it’s probably about 60% cash.”

Customers — especially millennials— don’t like using cash, and cash sitting in a back office isn’t secure. However, major banks and credit card companies still won’t touch cannabis. It remains a Schedule I drug, illegal at the federal level.

This creates a gap that Keith McCarty hopes to cash in on.

McCarty is CEO of Wayv (pronounced wave). The year-old company provides an Amazon-like platform for legal marijuana retailers in California to do online sales and next day delivery.

“We have well over 90 percent of the licensed retailers already ordering through Wayv, and more than 80 leading brands within the state of California,” McCarty said. [Read more at CNBC]