Trying to write the interface to gsl_multifit_fdfsolver_jac

I am trying to write the interface to this gsl function: gsl_multifit_fdfsolver_jac (I believe introduced in gsl 2.0) that is necessary for nonlinear-least-squares.lisp

(It is returns the Jacobian) See documentation https://www.gnu.org/software/gsl/manual/html_node/Computing-the-covariance-matrix-of-best-fit-parameters.html#Computing-the-covariance-matrix-of-best-fit-parameters and example usage:

gsl_multifit_fdfsolver_jac(s, J); gsl_multifit_covar (J, 0.0, covar);

This is my failed attempt after looking at gsll code and documentation

(defmfun jacobian (solver) "gsl_multifit_fdfsolver_jac" (((mpointer solver) :pointer) (*jacobian :pointer) :definition :function :inputs (solver) :outputs (*jacobian) :c-return :success-failure :return ((make-foreign-array-from-mpointer *jacobian)) :documentation "Query the solver for the Jacobian, a pointer")

Can someone tell me how to make this work?

Thanks,

Mirko