Hello,
The code below works perfectly without the placement of the label, but if I
want to place the label, it no longer works.
Thank you

\definefloat
   [recipe]
   [figure]

\setupfloat
   [recipe]
   [default={right,none}]

\starttext

\switchtobodyfont [pagella, 9pt]

\placerecipe{}{

\startMPcode

pair vert[] ;
n:=6 ; radius=2cm ;
for i=0 upto n :
        vert[i] = radius * dir(360*i/n) ;
endfor ;

draw for i=0 upto n-1: vert[i] -- endfor cycle withcolor blue ;

draw for i=0 upto n-1: vert[i] .. endfor cycle withcolor red ;

draw (0,0)--vert[0] withcolor green ;

draw (0,0)--vert[5] withcolor green ;

draw (0,0) --(vert[0]+vert[5])/2 dashed evenly ;

% label.urt("C",vert[1])  ;


\stopMPcode
}

\input knuth

\stoptext