Won't allow me create shortlink with letters.

[ghost]

Hello, I've been trying to create shortlinks with letters such as.

Short.link/1500va

But when I save the shortlink it comes out as 'short.link/1500', I've also tried to just use letters but comes up with warning stating that I need to type something. So it only works with numbers and nothing else.

[dgw]

Sure sounds like https://github.com/josheby/yourls-additional-charsets in 10 mode (digits only).