Exponential fitting for multiple curves forcing the curves to pass through one point (xo,yo)

I want to make different curves (existing in an array) fit an exponential function passing through a point (different for each curve).

When I do the fit for a single curve, I have no problem (in fact, I follow the guidelines in this question https://fr.mathworks.com/matlabcentral/answers/424475-how-to-force-a-exponential-fit-to-go-through-a-preestablish-point-x-y). Which means:

ft = fittype('y0*exp(b*(x-x0))','independent','x',...  
'problem',{'x0','y0'},'coefficients','b');
x0 = 0;
y0 = 2;
mdl = fit(x,y,ft,'problem',{x0,y0},'StartPoint',0.5);

My problem is when I try to solve the fit for each of the curves in the array x and y. Here is the way I approach the problem:

ft= fittype('y0*exp(b*(x-x0))','independent','x',...
   'problem',{'x0','y0'},'coefficients','b');
x0=cell(1,length(x));
y0=cell(1,length(x));
mdl=cell(1,length(x));
for k = 1:length(x)
        x0{k}=x_max_1stder_jun_17_s{k}; %Xo points
        y0{k}= y_max_1stder_jun_17_s{k}; %Yo points
        mdl{k}= fit(x{k},y{k},ft,'problem',{x0{k},y0{k}},'StartPoint',0.5);
end

Any clues as to what I am doing wrong?

Thank you in advance!

[Torsten]

What is the error message ?

[Angelavtc]

oh la la, now it seems that thre is nor problem anymore. So strange... anyway, thank you @Torsten