Cryptocurrency exchange Bitfinex, one of the largest cryptocurrency exchanges in the world, announced on Wednesday that it has removed a Georgia post card issued by the United States Postal Service from its website.

According to a post on the company’s blog, the Georgia postcards had been removed due to “security concerns” with the Georgia state agency that manages the USPS, which the postcard was sent to.

BitfineX said it is investigating how the postcards were placed on its platform.

Georgia is one of several states where Bitcoin is used to pay for goods and services.

The USPS website was previously inaccessible due to an outage caused by the agency’s massive wildfire response, but it has since returned to normal.

A spokesperson for the Georgia Department of Economic and Community Development said in a statement that the USPS has a strict policy on postcards, and the agency had “received complaints” about the Georgia card.