The North American Bitcoin Conference, which will take place in Miami next week, is no longer allowing people to pay for tickets with cryptocurrencies due to “network congestion and manual processing” issues. The ticketing page for the conference notes that it had accepted such forms of payment up until 14 days before the event, but that bitcoin transactions would not be possible for last-minute buyers because of “print deadlines.”

Moe Levin, the conference’s organizer, told Bitcoin.com, “We wish this was easier, but no ticketing options exist which can handle large volumes of ticket sales, and transaction fees on the Bitcoin blockchain exceed $30 at certain times of the day.” His team is reportedly trying to find a way to implement cryptocurrencies with lower transaction fees, such as bitcoin cash, into the payment system. Yet, as Levin notes, it’s difficult to set up crypto payments when ticketing services like Eventbrite don’t accept bitcoin yet.

The news underscores concerns that Bitcoin is, at the moment, virtually useless for making payments. A number of vendors have actually stopped accepting it for purchases due to its wildly fluctuating value and high transaction fees.

Microsoft, which integrated a bitcoin payments system in 2014, temporarily suspended transactions using the cryptocurrency in the company’s online store this week due to instability. In December, the popular video game purchasing platform Steam announced that it would no longer accept bitcoin, also because of volatility and prohibitive fees.