Rinkeby – How to Deploy Smart Contracts to Rinkeby Testnet

I'm getting the following error when I try to deploy my smart contract to Rinkeby using Truffle:

Error: Unknown arguments format passed to new HDWalletProvider. Please check your
configuration and try again

Note: I haven't had any problems deploying this same contract locally using Truffle, only to Rinkeby.

Here's my code:

require('dotenv').config();
const HDWalletProvider = require('@truffle/hdwallet-provider');  

module.exports = {
  networks: {
     development: {
        host: "127.0.0.1",     
        port: 8545,            
        network_id: "*",   
     },

     rinkeby: {
        provider: () => new HDWalletProvider(process.env.RINKEBY_MNENOMIC, 
        "https://rinkeby.infura.io/v3/${process.env.INFURA_API_KEY}"),
         host: "127.0.0.1", 
         network_id: 4,
         gas: 4612388,
         gasPrice: 10000000000
     },
 },

 // Configure your compilers
 compilers: {
    solc: {
       version: "0.6.2",  
    }
 }

}

I'm wondering if this is some sort of version issue cause I'm seeing that my previous contracts used 'truffle-hdwallet-provider', while this one is using '@truffle/hdwallet-provider'

Meanwhile, my .env file contains the following:

#MNENOMIC="word1 word2 word3, ...word12"
RINKEBY_MNENOMIC="word1 word2 word3, ...word12"
PRODUCTION_MNENOMIC="word1 word2 word3, ...word12"

INFURA_API_KEY="xxxxxxxxxxxxxxxxxxxx"

So what might be happening here? What is this Unknown arguments format passed to new HDWalletProvider error all about?