Api-gateway custom domain names: Bug in valid domain checking

If I navigate to Api Gateway -> Custom domain names -> create, and enter 'api.exampl.com' in the domain name field, choose 'Regional' endpoint type, select an ACM certificate, and click the 'Create domain name' button, I get the following error banner at the top of my screen:

Invalid domain name api.exampl.com. Valid patterns are ^*[\w\d-]*.(([\w\d-]+.)+[\w\d-]+)$ or ^(([\w\d-]+.)+[\w\d-]+)$

It seems like this should be an acceptable domain name, matching the above regular expression. I'm using Google Chrome 100.0.4896.127 on Ubuntu 20.04. I have two APIs defined in API gateway