TOKEN VALIDATION FAILED - MLE

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TOKEN VALIDATION FAILED - MLE

Account Validation API with MLE call error out with "code:9212 and message: Token validation failed". 

Here are the details - 
URL - https://sandbox.api.visa.com/pav/v1/cardvalidation

JWE header =  var header = new Dictionary<string, object>{
{ "iat", DateTime.UtcNow.ToString()} ,
{ "kid", "3d9XXXXXXXXXXXXXXXX418"},
{ "alg", "RSA-OAEP-256" },
{ "enc", "A128GCM" },
{ "cty" , "application/json" },
};
Request Body - payload is encrypted with a public key got from Visa developer portal.

Response - {"responseStatus":{"status":401,"code":"9212","severity":"ERROR","message":"Token validation failed","info":""}}

Could you please suggest what are we doing wrong here? We have followed the steps mentioned in the encryption guide.

Also, please share the error descriptions for all the codes returned by 401 such as 9212, 9208, 9209.