Dear All, I would like to introduce constraints in the MultiNonlinearModelFit function.I have followed the usual format for declaring constraints as shown below but it seems to be problematic.

fit = MultiNonlinearModelFit[{Abs380, Abs450, 
    Abs490}, {model380[k3, kr3, k4, k5, kr5, ea380, eh380, ef380, 
      erS380][t], 
    model450[k3, kr3, k4, k5, kr5, ea450, eh450, ef450, erS450][t], 
    model490[k3, kr3, k4, k5, kr5, ea490, eh490, ef490, erS490][t], 
    k4 > 640000, k5 < 0.1, 
    kr5 > 15000}, {{k3, 36}, {kr3, 0.4}, {k4, 700000}, {k5, 
     0.07}, {kr5, 16000}, {ea380, 6200}, {eh380, 8200}, {ef380, 
     12800}, {ea450, 8500}, {eh450, 2400}, {ef450, 2800}, {ea490, 
     5400}, {eh490, 1200}, {ef490, 3000}, {erS380, 4500}, {erS450, 
     2700}, {erS490, 1000}}, {t}];

Does the MultiNonlinearModelFit function allow constraints on parameters? Looking at the function in detail, the answer to this question seems positive but I don't understand why mathematica doesn't understand the code. Note that the message appears as soon as I add these constraints. Thank in advance for all your advices. Best Hélène