In a flow add character to string

[flows-daniel (Daniel Kimmelmann)]

Try this then:

$length($string(OrgNo)) = 10 ? $split($string(OrgNo),/.{4}$/,3)[0] & "-" & $split($string(OrgNo),/.{6}/,3)[1] : OrgNo

If the length equals 10 then perform the logic to split it, if the length is anything else, then return the whole number.