Cannot insert the mapsto character ↦ in groff

I am trying to learn how to insert the mapsto (↦, U+21A6) character in groff. I am trying to use this code to insert the character

\[u21A6]

But I get the following error message and nothing is inserted in the output file:

troff: doc.ms:40: warning: can't find special character 'u21A6'

I have tried to follow multiple tutorials and read some documentation, but could not find a solution to the problem. What am I doing wrong? (by the way I tried with and without the -Kutf8 option, as well as inserting the Unicode character ↦ as is in the file) Here is a document example (file test.ms):

.TL
document
.LP
a \[u02DA] b

a ↦ b

.EQ
define maps_to % ↦ %
a maps_to b
.EN

And the command line I use is:

groff -e -ms -Kutf8 test.ms | gv -