ERROR: LoadError: Need an adjoint for constructor EnsembleSolution

[yanz4]

I wish to use Flux.training to optimize a parameter in parallel ensemble simulation defined by EnsembleProblem() provided by DifferentialEquations.jl. The output I expect is the gradient output with respect to the tracked parameter. However, it shows that there's no adjoint method provided as below:

ERROR: LoadError: Need an adjoint for constructor EnsembleSolution{Float64,2,Array{ODESolution{Float64,1,Array{Float64,1},Nothing,Nothing,Array{Float64,1},Array{Array{Float64,1},1},ODEProblem{Float64,Tuple{Float64,Float64},false,DiffEqBase.NullParameters,ODEFunction{false,var"#16#17",LinearAlgebra.UniformScaling{Bool},Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing},Base.Iterators.Pairs{Symbol,QuadratureAdjoint{0,true,Val{:central},Bool},Tuple{Symbol},NamedTuple{(:sensealg,),Tuple{QuadratureAdjoint{0,true,Val{:central},Bool}}}},DiffEqBase.StandardODEProblem},Tsit5,OrdinaryDiffEq.InterpolationData{ODEFunction{false,var"#16#17",LinearAlgebra.UniformScaling{Bool},Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing,Nothing},Array{Float64,1},Array{Float64,1},Array{Array{Float64,1},1},OrdinaryDiffEq.Tsit5ConstantCache{Float64,Float64}},DiffEqBase.DEStats},1}}. Gradient is of type Array{Float64,2}

My simplified code is attached as below. I'd be grateful of any insights.

using DifferentialEquations, Flux, DiffEqSensitivity
 

pa = [1.0]

function model1(input) 
  prob = ODEProblem((u, p, t) -> 1.01u * pa[1], 0.5, (0.0, 1.0), sensealg = QuadratureAdjoint())
  
  function prob_func(prob, i, repeat)
    remake(prob, u0 = rand() * prob.u0)
  end
  
  ensemble_prob = EnsembleProblem(prob, prob_func = prob_func)
  sim = solve(ensemble_prob, Tsit5(), EnsembleThreads(), trajectories = 100)

end

Input_time_series = zeros(5, 100)

loss(x, y) = Flux.mse(model1(x), y)

data = Iterators.repeated((Input_time_series, 0), 1)
 
gs = Flux.gradient(() -> loss(Input_time_series, 0), params(pa)) 

[CarloLucibello]

the adjoint should be defined wherever EnsembleProblem is defined, so better move this issue over to DifferentialEquations