Detector fails to link Slack notification silently

[blkperl]

The Slack notification is silently failing. The Pagerduty one is linked but the Slack one is not linked when I look at them in the SignalFX UI.

This is the code that I have that creates the detectors.

resource "signalform_detector" "site_capacity" {
    provider = "signalform"
    count = "${length(var.regions)}"
    name = "${var.regions[count.index]} stack capacity"
    max_delay = 30
    description = "Alerts when stack capacity in a region is full"
    program_text = <<-EOF
        [.....]
        detect("Site Capacity @ 95%", when(site_count > site_capacity * 0.95, lasting='5s'))
        detect("Site Capacity @ 90%", when(site_count > site_capacity * 0.90, lasting='5s'))
    EOF
    rule {
        description = "active when site count exceeds 95% site capacity"
        severity = "Critical"
        detect_label = "Site Capacity @ 95%"
        notifications = ["PagerDuty,RedactedId"]
    }
    rule {
        description = "active when site count exceeds 90% site capacity"
        severity = "Major"
        detect_label = "CDE Site Capacity @ 90%"
        notifications = ["Slack,RedactedId,#channelname"]
    }
}