Joi date validation not working on greater than

I have this joi validation schema

  requiredInceptionDate: Joi.date().format("DD/MM/YYYY").raw(),
  requiredExpiryDate: Joi.date()
    .format("DD/MM/YYY")
    .raw()
    .min(Joi.ref("requiredInceptionDate")),

however I get this error

Error: ValidationError: "requiredExpiryDate" must be greater than or equal to "ref:requiredInceptionDate"

the file I’m processing has

  "requiredInceptionDate":"01/09/2021",
  "requiredExpiryDate":"30/10/2022",

All i can think of is perhaps it doesn’t like the fact it’s a string? But that’s why I used raw()