In the description of the Staff of Frost (DMG, pg. 202), the following is included in its description, detailing spells that can be cast with charges from the staff:
The staff has 10 charges. While holding it, you can use an action to expend 1 or more of its charges to cast one of the following spells from it, using your spell save DC: cone of cold (5 charges), fog cloud (1 charge), ice storm (4 charges), or wall of ice (4 charges).
That last spell, wall of ice, is a 6th level spell. It should cost 6 charges, shouldn't it? All of the other spells cost a number of charges equal to their spell level (ice storm is a 4th level spell so it costs 4 charges, cone of cold is a 5th level spell so it costs 5 charges, etc).
But not wall of ice, which costs only 4 charges, making it "cheaper" than casting cone of cold, even though wall of ice is a 6th level spell and cone of cold only a 5th level spell.
Do we know if this is a mistake? Has this received errata?
Best Answer
As NautArch's answer says, your quote of the description of the staff of frost is correct; it has not been changed as of the 2019 DMG errata.
In addition, as Michał Politowski points out in a comment on that answer, rules designer Jeremy Crawford unofficially confirmed in a 2016 tweet that the charge cost of the wall of ice spell for that magic item is not a mistake:
Thus, given that the cost is intentional, it is unlikely to be changed in errata.