Cannot compute gradient operator

Question

I am trying to make a VQC with amplitude encoding(2000~ feature ) so i cant use the usual ZZfeature map ..instead i am using RawFeatureVector but when i use it to construct the VQC object it shows the error 'Cannot compute gradient operator! Continuing without gradients!'

note: i did try the ZZfeature and the error goes away so i know that the problem is here.

qc = RawFeatureVector(4)
qc.num_qubits #outputs 2 

var_circuit = EfficientSU2(2, reps=2)
my_opt = COBYLA(maxtir=500 , tol=0.001)
vqc = VQC(optimizer=my_opt , feature_map =qc , ansatz = var_circuit )

EDIT: the RawFeatureVectordose not support gradient based optimizers ..although COBYLA and SPSA ara gradient free so you can use them (even if you still gets the warning )