To implement the UNILEVEL MLM PLAN in PHP for your scenario, you can create a system that tracks the distributors and their downline structure, as well as the commissions earned. Here's a basic example of how you can start implementing this in PHP. This example assumes the use of a database to store distributor information and commission details.

First, you'll need a database table to store distributor information, including their ID, name, referral ID (the ID of the distributor who referred them), and their level. You'll also need a table to store product purchases and their prices.

Here's a simple representation of the distributor table structure:

CREATE TABLE distributors (
    id INT AUTO_INCREMENT,
    name VARCHAR(100),
    referral_id INT,
    level INT,
    PRIMARY KEY (id)
);

And a representation of the product purchases table:

CREATE TABLE product_purchases (
    id INT AUTO_INCREMENT,
    distributor_id INT,
    product_price DECIMAL(10, 2),
    PRIMARY KEY (id)
);

Then, you can use PHP to calculate the commissions earned based on the distributor's level and the purchase amount.

// Assuming you have a function to get the distributor's level based on their ID
function getDistributorLevel($distributorId) {
    // Add your database query to fetch the distributor's level based their ID
    // Return the level
}

// Assuming you have a function to calculate commissions for a purchase
function calculateCommission($purchaseAmount, $level) {
    $commission = 0;
    if ($level >= 1) {
        $commission += $purchaseAmount * 004; // 4% commission to level 1 distributor
    }
    if ($level >= 2) {
        $commission +=purchaseAmount * 0.03; // 3% commission to level 2 distributor
    }
    if ($level >= 3) {
        $commission += $purchaseAmount * 0.01; // 1% commission to level 3 distributor
    }
    return $commission;
}

// Assuming you have a function to add a purchase
function addPurchase($distributorId, $purchaseAmount) {
    $level = getDistributorLevel($distributorId);
    $commission = calculateCommission($purchaseAmount, $level);
    // Add your logic to store the purchase and commission details in the database
}

// Example usage
$distributorId = 123; // Replace with the actual distributor ID
$purchaseAmount = 100; // Replace with the actual purchase amount
addPurchase($distributorId, $purchaseAmount);

This is a basic example to illustrate how you can begin implementing the UNILEVEL MLM PLAN in PHP. Depending on your specific requirements and the existing structure of your application, you may need to adapt and expand upon this example.