How can I encrypt a sensitive data using Apple's newer CryptoKit library which is then decrypted by the older SecKeyCreateDecryptedData?

Question

Given the decryption below which is using the older API of SecKeyCreateDecryptedData. (This has been proved end-to-end with backend that it works with their implementation of encryption.) I was checking this article during implementing the decryption back then.

let appEphPrivSecKey: SecKey = ...
let serverEphPubKeyData: Data = ...
let encryptedDataFromServer: Data = ...

var fullEncryptedData = serverEphPubKeyData
fullEncryptedData.append(contentsOf: encryptedDataFromServer) // so that we have the required format of ephemeral public key + ciphertext + tag
 
var unmanagedError: Unmanaged<CFError>?
let decryptedData = SecKeyCreateDecryptedData(
     appEphPrivSecKey,
     .eciesEncryptionCofactorVariableIVX963SHA256AESGCM,
     fullEncryptedData as CFData,
     &unmanagedError)

How can I implement the encryption part, but using the newer CryptoKit library provided by Apple?

---

I tried almost each and every combination, but never managed to make it work (neither with backend nor with my old decryption). This is one example of my tests:

let appEphPrivSecKey: SecKey = ...
let serverEphPubKeyData: Data = ...

let appEphemeralPrivKeyData = SecKeyCopyExternalRepresentation(appEphPrivSecKey, nil)! as Data
let appEphemeralPrivKey = try P256.KeyAgreement.PrivateKey(x963Representation: appEphemeralPrivKeyData)
        
let serverEphemeralPublicKey = try P256.KeyAgreement.PublicKey(x963Representation: serverEphPubKeyData)
        
let sharedSecret = try appEphemeralPrivKey.sharedSecretFromKeyAgreement(with: serverEphemeralPublicKey)
        
let derivedSymmetricKey = sharedSecret.x963DerivedSymmetricKey(
     using: SHA256.self,
     sharedInfo: appEphemeralPrivKey.publicKey.x963Representation,
     outputByteCount: 16)
        
let sealedBox = try AES.GCM.seal(sensitiveData, using: derivedSymmetricKey)
        
let encryptedData = sealedBox.ciphertext + sealedBox.tag

But this does not work, I always receive the error below: The operation couldn’t be completed. (OSStatus error -50 - ECIES: Failed to aes-gcm decrypt data (err -69))