Chainlink Function Computation Error: 'Error: input into Functions.encodeString is invalid'

In short:

• Been trying to access any data from a particular, chosen API url.
• Can view the JSON in browser, but can't call variable in Remix (which should change after SendRequest).
• Tried a wide variety of scenarios (from trying to access different values at the endpoint URL, or trying to access different data types from endpoint, etc), just to validate that I can access data from this URL. I.e. If I can access anything, then I can eventually access the data I want for the Block Magic Hackathon.
• Ideally, what I expect: String variable which was undefined when contract deployed, now has data when called in Remix (and this change should occur after using SendRequest function).

Source of the Error:

In functions.chain.link/polygon-amoy/ 'History' of Recent Fulfillments, the Callback function gives me a Green Tick, but the Computation shows an error:

Error: input into Functions.encodeString is invalid

Here is the API URL I am trying to access:

Note: I'm currently using my API Key in the URL for testing, and will move onto using Secrets in Chainlink Functions after I get this initial testing to fire. Thus this is the URL with the API Key removed:

https://api.sportmonks.com/v3/football/fixtures/date/2024-05-15&includes=scores

Here is my full, current test smart contract, only with the API URL switched out:

pragma solidity 0.8.19;

import {FunctionsClient} from "@chainlink/[email protected]/src/v0.8/functions/v1_0_0/FunctionsClient.sol";
import {ConfirmedOwner} from "@chainlink/[email protected]/src/v0.8/shared/access/ConfirmedOwner.sol";
import {FunctionsRequest} from "@chainlink/[email protected]/src/v0.8/functions/v1_0_0/libraries/FunctionsRequest.sol";

/**
 * Request testnet LINK and ETH here: https://faucets.chain.link/
 * Find information on LINK Token Contracts and get the latest ETH and LINK faucets here: https://docs.chain.link/resources/link-token-contracts/
 */

/**
 * @title GettingStartedFunctionsConsumer
 * @notice This is an example contract to show how to make HTTP requests using Chainlink
 * @dev This contract uses hardcoded values and should not be used in production.
 */
contract GettingStartedFunctionsConsumer is FunctionsClient, ConfirmedOwner {
    using FunctionsRequest for FunctionsRequest.Request;

    // State variables to store the last request ID, response, and error
    bytes32 public s_lastRequestId;
    bytes public s_lastResponse;
    bytes public s_lastError;

    // Custom error type
    error UnexpectedRequestID(bytes32 requestId);

    // Event to log responses
    event Response(
        bytes32 indexed requestId,
        string unknownVar,
        bytes response,
        bytes err
    );

    // Router address - Hardcoded for Sepolia
    // Now hardcoded for Amoy
    // Check to get the router address for your supported network https://docs.chain.link/chainlink-functions/supported-networks
    address router = 0xC22a79eBA640940ABB6dF0f7982cc119578E11De;

    // JavaScript source code
    // Fetch character name from the Star Wars API.
    // Documentation: https://swapi.info/people
    string source =
        "const apiResponse = await Functions.makeHttpRequest({"
        "url: 'API_URL_WITH_REQUIRED_API_KEY'"
        "});"
        "if (apiResponse.error) {"
        "console.log('There was an error, sorry.');"
        "throw new Error('Request failed, sorry.');"
        "}"
        "let dataPoint1 = apiResponse.data.id;"
        "console.log(dataPoint1);"
        "return Functions.encodeString(dataPoint1);";

    //Callback gas limit
    uint32 gasLimit = 300000;

    // donID - Hardcoded for Sepolia
    // Now hardcoded for Amoy
    // Check to get the donID for your supported network https://docs.chain.link/chainlink-functions/supported-networks
    bytes32 donID =
        0x66756e2d706f6c79676f6e2d616d6f792d310000000000000000000000000000;

    // State variable to store the returned character information
    string public unknownVar;

    /**
     * @notice Initializes the contract with the Chainlink router address and sets the contract owner
     */
    constructor() FunctionsClient(router) ConfirmedOwner(msg.sender) {}

    /**
     * @notice Sends an HTTP request for character information
     * @param subscriptionId The ID for the Chainlink subscription
     * @param args The arguments to pass to the HTTP request
     * @return requestId The ID of the request
     */
    function sendRequest(
        uint64 subscriptionId,
        string[] calldata args
    ) external onlyOwner returns (bytes32 requestId) {
        FunctionsRequest.Request memory req;
        req.initializeRequestForInlineJavaScript(source); // Initialize the request with JS code
        if (args.length > 0) req.setArgs(args); // Set the arguments for the request

        // Send the request and store the request ID
        s_lastRequestId = _sendRequest(
            req.encodeCBOR(),
            subscriptionId,
            gasLimit,
            donID
        );

        return s_lastRequestId;
    }

    /**
     * @notice Callback function for fulfilling a request
     * @param requestId The ID of the request to fulfill
     * @param response The HTTP response data
     * @param err Any errors from the Functions request
     */
    function fulfillRequest(
        bytes32 requestId,
        bytes memory response,
        bytes memory err
    ) internal override {
        if (s_lastRequestId != requestId) {
            revert UnexpectedRequestID(requestId); // Check if request IDs match
        }
        // Update the contract's state variables with the response and any errors
        s_lastResponse = response;
        unknownVar = string(response);
        s_lastError = err;

        // Emit an event to log the response
        emit Response(requestId, unknownVar, s_lastResponse, s_lastError);
    }
}

Thanks for any time and assistance you can provide.

Happy to reply where I can, if further context or clarification is required.