CHW-4402 BillingCycleInvalid
billing_cycle must be either "month" or "year"
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Default message: billing_cycle must be either “month” or “year”
HTTP status:400(client)
Problem. /api/billing/checkout rejected the supplied
billing_cycle. Cause. Value was not "month" or "year"; we
only sell those two cadences. Fix. Supply one of the two accepted
strings (defaults to "month" if omitted). HTTP 400.