solve a system of equations symbolically

I want to solve a system of equations that consist of 5 equations and 11 unknowns as mentioned later. the equations are:

And the unknowns are:

I have to determine in terms of the .

I've written the following code:

syms S1 S2 S3 A1 A2 A3 B1 B2 B3 M21 M32
eqn=[A1*sinh(S1)+B1*sinh(S1)-B2==0, A2*sinh(S2)+B2*cosh(S2)-B3==0, A3*sinh(S3)+B3*cosh(S3)==0, A1*cosh(S1)+B1*sinh(S1)-A2*M21==0, A2*cosh(S2)+B2*sinh(S2)-A3*M32==0];
S= solve(eqn, [A2 A3 B1 B2 B3]) 

But I can not see results for .

Could you please guide me on how could I determine in terms of the ?