First word is a giveaway. More an excise in typing.
The key is given in white font. Select text or cut and paste to read. Letters not used in the message are indicated by "?":
_CODE -> _PLAIN
A -> ?
B -> D
C -> F
D -> ?
E -> N
F -> ?
G -> ?
H -> R
I -> ?
J -> ?
K -> A
L -> S
M -> Y
N -> Z
O -> P
P -> E
Q -> M
R -> K
S -> G
T -> V
U -> H
V -> O
W -> I
X -> T
Y -> U
Z -> L