In the second question of the library/full name question, how do I write the concatenation SQL statement?

In this problem, I'm being asked to query two columns from a table, the first being concatenated from two columns of text. In this question, I have concatenated using all three forms of code provided earlier. Here are the other two:

SELECT first_name || ' ' || UPPER(last_name) AS full_name, library_id FROM patrons

SELECT CONCAT(first_name, " ", UPPER(last_name)) AS full_name, library_id FROM patrons

I cannot for the life of me figure out what I'm doing wrong, as the quiz only tells me "there's something wrong with your SQL code." What am I doing wrong?