The following is an example of a smart contract using Chainlink.Request to make a call to a Covalent API pricing endpoint. This example is adapted from the one found on Chainlink’s docs - refer to this in order to get details of the contract setup.

The process is as follows:

1. Identify the appropriate Chainlink node to use from https://market.link/search/jobs for the required response data format and note the oracle address and jobId and fee. In the example below, we are using a Get > Uint256 node on the Kovan testnet to get pricing data in Uint256.
2. Set the oracle node address, jobId and fee in the constructor.
3. Use the appropriate Covalent API URL in request.add(...)
4. Parse the response with the path string array as shown
5. Compile and deploy the contract. Note the contract address.
6. Send the contract address some LINK tokens. You can find a list of LINK testnet faucets here.
7. Call the getETHPrice() method
8. Call the price variable to get the ETH price in the smart contract fetched via the Covalent API!

Example smart contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "@chainlink/contracts/src/v0.8/ChainlinkClient.sol";

contract CovalentAPIConsumer is ChainlinkClient {
    using Chainlink for Chainlink.Request;
  
    uint256 public price;
    
    address private oracle;
    bytes32 private jobId;
    uint256 private fee;
    
    /**
     * Network: Kovan
     * Oracle: 0xc57B33452b4F7BB189bB5AfaE9cc4aBa1f7a4FD8 (Chainlink Devrel   
     * Node)
     * Job ID: d5270d1c311941d0b08bead21fea7747
     * Fee: 0.1 LINK
     */
    constructor() {
        setPublicChainlinkToken();
        oracle = 0xc57B33452b4F7BB189bB5AfaE9cc4aBa1f7a4FD8;
        jobId = "d5270d1c311941d0b08bead21fea7747";
        fee = 0.1 * 10 ** 18; // (Varies by network and job)
    }
    
    function getETHPrice() public returns (bytes32 requestId) 
    {
        Chainlink.Request memory request = buildChainlinkRequest(jobId, address(this), this.fulfill.selector);
        
        // Set the URL to perform the GET request using the Covalent API
        request.add("get", "<https://api.covalenthq.com/v1/pricing/tickers/?quote-currency=USD&format=JSON&tickers=ETH&key=ckey_docs>");
				
				/* The response looks like:
				data: {
					items: [
						{
							...
							quote_rate: 3101.778,
							...
						}
				*/

        string[] memory path = new string[](4);
        path[0] = "data";
        path[1] = "items";
        path[2] = "0";
        path[3] = "quote_rate";
        request.addStringArray("path", path);
        
        // Sends the request
        return sendChainlinkRequestTo(oracle, request, fee);
    }
    
    /**
     * Receive the response in the form of uint256
     */ 
    function fulfill(bytes32 _requestId, uint256 _price) public recordChainlinkFulfillment(_requestId)
    {
        price = _price;
    }

    // function withdrawLink() external {} - Implement a withdraw function to avoid locking your LINK in the contract
}