help with regular expression allowing exactly 9 digits

[Ronald5DCA]

Hi,

Im trying to add a form field for an TAX ID which is exactly 9 digits.  I am entering it as shows in the attachment but it is not working.  Any help would be greatly appreciated.

[Enchanted_difference1549]

I know this is an old post, anyway for the records: 

even now (feb 2024) this is not working and it's probably some kind of bug in regexp parsing by Sign, because the syntax is working when combined in more complex formulas, anyway you can use a working synonym as:

^[0-9]{6}$

this works. Why not the other? Dunno.