"Technical difficulties" have caused delays for people buying tickets for this year's National Eisteddfod.
Some have taken to social media to express their frustration at not being able to book tickets for events.
The Wales Millennium Centre, which is selling tickets for the arts festival, has apologised for the disruption.
The National Eisteddfod also apologised on Twitter, saying the centre had experienced "technical difficulties" and "high volumes" to its website.
It continued: "Keep trying and thank you for your patience!"
The initial technical problem has been resolved and the Wales Millennium Centre says it has its "teams working hard on the phones".
Tickets went on sale for the event in Cardiff at 08:30 BST.
Bore da! @theCentre are experiencing high volumes to their website and some technical difficulties. Keep trying and Thank you for your patience!— National_Eisteddfod (@Eisteddfod_eng) April 3, 2018
Sarah Nicholas said on Twitter: "I've got through on the phone 18 times, but I'm always cut off.
"I'm really, really sad about this."
2.5 hours into this thing and I'm going to give up. I've got through on the phone 18 times, but am always cut off. I can't make it past the confirm payment page online. I'm really, really sad about this. I so wanted to give an Eisteddfod concert a try. 😢— Sarah Nicholas (@SarahNicholas) April 3, 2018
The National Eisteddfod said the booking process was still slow, but encouraged users to "please persevere".
The Eisteddfod will be held in Cardiff from 3-11 August.