I have attempted to purchase 2 online tickets from Canada for July 23/17 at 1:00pm over the past two days. I get all the way through the purchase process, and then once I have entered my payment info, I get a large red "ERROR" message. I realize that Sundays after 3pm are free, but we wanted to go that day, earlier, and are ok with purchasing tickets. I purchased tickets for Sagrada Familia with the same credit card and no problems. I note from searching the travel forum that similar problems were experienced about 3-4 years ago. Any suggestions?
Perhaps try using PayPal if that's an option? Or a different credit card? Issues like this pop up from time to time (related to various sights or train tickets), and we don't always know what the problem is.
I just purchased tickets for Picasso museum and the transaction went through fine. Possibly try different browser? I used Safari.
Have you checked with your credit card company to see if the transaction went through? Sometimes, my first online purchase in a foreign country goes through without difficulty, but they then block the next transaction.
If your credit card company is not blocking the transaction, I also second the suggestions of PayPal and of trying a different browser.
Thank you everyone for your helpful suggestions. I have just successfully purchased tickets to the Picasso Museum for July 23/17 with an audio guide! I used the browser on my phone and a different credit card (from the previous attempts) to make the purchase. I will definitely check with my bank to make sure there are no issues with my credit cards before we leave for Europe on July 13/17. Thanks again to the great Rick Steves travelling community!