reftype 0 means Unknown
The slot refreshes, but the trigger is unknown or not reported; this is the default when reftype is absent.
When to send it
Send 0, or omit reftype, when you know a slot refreshes but cannot say why, for example when a publisher's own script reloads the tag and the SSP only sees the repeated requests. It goes in RefSettings.reftype inside imp.refresh.refsettings, and RefSettings.minint still applies if you know the interval.
Buyers usually treat an unknown trigger cautiously and may price it like the least valuable refresh type they support. It is confused with sending no refresh object at all, which means the seller makes no claim about refresh. Do not use 0 for a slot that never refreshes; leave Imp.refresh out instead.
Example
{
"imp": [
{
"refresh": {
"refsettings": {
"reftype": 0
}
}
}
]
}Fields that carry it
Other values in auto refresh triggers
The auto refresh triggers list page explains the whole list and its common mistakes.