@appnet Use an acf/validate_value filter similar to what I suggested here https://support.advancedcustomfields.com/forums/topic/check-number-when-saving/
There may be a way to do this by altering the select2 arguments, see the select2_init section. Unfortunately, I don’t know if this is possible or how to do so if it is.
Beyond this it would take the developer adding this feature. You can request this by submitting a new ticket here https://support.advancedcustomfields.com/new-ticket/
