problem with using function ikine6s()

[東南]

Hello everyone, I am doing my work with RTB and I have a problem when using it. I want to do the inverse kinematic with the function ikine6s(), and the code is:

clear all;

clc;

% theta   d   a   alpha   

SL1 = Link([0   615   250    -pi/2], 'standard'); 

SL2 = Link([0    0    870      0  ], 'standard');

SL3 = Link([0    0    170    -pi/2], 'standard');

SL4 = Link([0   1016   0      pi/2], 'standard');

SL5 = Link([0    0     0     -pi/2], 'standard');

SL6 = Link([0   216    0       0  ], 'standard');

robot = SerialLink([SL1 SL2 SL3 SL4 SL5 SL6], 'name', 'robot');

figure(1),teach(robot);

T = robot.fkine([pi/6 -pi/2 pi/4 pi/3 pi/6 pi/4])

q = robot.ikine6s(T);

q = rad2deg(q)

and the error information is:

This kinematic structure not supported

How can I solve this problem?