cannot differentiate foreigncall expression

ERROR: LoadError: Can't differentiate foreigncall expression
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] get at ./abstractdict.jl:598 [inlined]
 [3] (::typeof(∂(get)))(::Nothing) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [4] accum_global at /home/cody/.julia/packages/Zygote/YeCEW/src/lib/lib.jl:59 [inlined]
 [5] (::typeof(∂(accum_global)))(::Nothing) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [6] #118 at /home/cody/.julia/packages/Zygote/YeCEW/src/lib/lib.jl:70 [inlined]
 [7] (::typeof(∂(λ)))(::Nothing) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [8] #216#back at /home/cody/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49 [inlined]
 [9] (::typeof(∂(λ)))(::Nothing) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [10] getindex at ./tuple.jl:24 [inlined]
 [11] gradindex at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/reverse.jl:12 [inlined]
 [12] #15 at /home/cody/Desktop/Research/Deep Learning/Flux files/PINN.jl:31 [inlined]
 [13] (::typeof(∂(λ)))(::Nothing) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [14] #49 at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface.jl:179 [inlined]
 [15] (::typeof(∂(λ)))(::NamedTuple{(:grads, :params),Tuple{IdDict{Any,Any},Nothing}}) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [16] gradient at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface.jl:55 [inlined]
 [17] (::typeof(∂(gradient)))(::NamedTuple{(:grads, :params),Tuple{IdDict{Any,Any},Nothing}}) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [18] f at /home/cody/Desktop/Research/Deep Learning/Flux files/PINN.jl:31 [inlined]
 [19] (::typeof(∂(f)))(::Float32) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [20] cost at /home/cody/Desktop/Research/Deep Learning/Flux files/PINN.jl:35 [inlined]
 [21] #17 at /home/cody/Desktop/Research/Deep Learning/Flux files/PINN.jl:37 [inlined]
 [22] (::typeof(∂(#17)))(::Float32) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:0
 [23] (::Zygote.var"#49#50"{Zygote.Params,Zygote.Context,typeof(∂(#17))})(::Float32) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface.jl:179
 [24] gradient(::Function, ::Zygote.Params) at /home/cody/.julia/packages/Zygote/YeCEW/src/compiler/interface.jl:55
 [25] top-level scope at /home/cody/Desktop/Research/Deep Learning/Flux files/PINN.jl:37
 [26] include(::String) at ./client.jl:439
 [27] top-level scope at REPL[4]:1
in expression starting at /home/cody/Desktop/Research/Deep Learning/Flux files/PINN.jl:37