The VISIBLE24 promo may not be combined with referral credits within the same month on the Visible plan as a $5/mo minimum charge is required ($20 Referral credits will apply first, instead of the $5 VISIBLE24 promo credits which will roll to the next month).
Go to https://www.visible.com/ and click on the information icon next to the VISIBLE24 promotion to see the fine print, but in general Visible has always had a minimum $5 billing policy. Keep track of any referral credits, the way I read it you should still get the $5 VISIBLE24 promo for 24 months (just not consecutive months).
