This is a result of the change made in the Fall patch to increase the faith cost of buying religious units. To compensate for the increased cost, each religious unit was given 1 additional charge. An apostle needs at least its default number of charges to evangelize a belief. Pre-patch that was 2 charges, and post-patch that's now 3 chargs, but Firaxis didn't update the tooltip, so it still (incorrectly) states that 2 charges are required.
If you have an apostle that has more than 3 charges (e.g., generated in a city with a mosque (+1 charge) or with the Orator promotion (+2 charges)) you can use the extra charges first and still evangelize a belief.