Openssl Encrypting and signing data using symmetric key in php

Question

The input is base64

byte[] encryptedContent = _crypto.AESEncrypt(input, key);
                string bContent = Convert.ToBase64String(encryptedContent);
                byte[] bSignature = _crypto.RSASign(Encoding.ASCII.GetBytes(bContent));
                request.Data.Content = bContent;
                request.Data.Signature = Convert.ToBase64String(bSignature);

Hello can someone help me to convert the above C# code to a php. Am trying to send an encrypted and a signed content to the server. but I get Data decryption error.

// encryption code 
$encrypt_json = openssl_encrypt(json_encode($Pjoson),
        "AES-128-GCM",
        "$SMKey");