Great to have you here, sblacket.
Alpha-numeric is a character that is either a letter or a number. In QuickBooks Online (QBO), the acceptable Alpha-numeric characters are A-Z, a-z, and 0-9.
For more details about acceptable characters in QBO, you can check out this article: https://quickbooks.intuit.com/learn-support/en-au/other-questions/acceptable-characters-in-quickbook....
Let me know if you need anything else in QBO. Just add more details by replying to this post.