Problem with adding a basic IF-statement to a code snippet

Question

I'm trying to add a basic IF-statement to a PHP code snippet but my PHP knowledge is very limited and I didn't have much success until now (I tried different variations on IF-statements which I found in other code snippets).

The company that originally created the code explained me in the code snippet where to add the IF-statement, what kind of IF-statement I need (if the coupon code begins with 'affiliate-credit' return true) and also told me I should work with the variable called $coupon (this variable contains the name of the coupon).

Here is the code snippet:

<?php
/**
 * Plugin Name: AffiliateWP - Block WooCommerce Assigned Affiliate Coupon If Affiliate Purchasing
 * Plugin URI: http://affiliatewp.com
 * Description: Prevents assigned affiliate coupon codes from being used on the WooCommerce order if the affiliate is the purchaser
 * Author: AffiliateWP
 * Author URI: https://affiliatewp.com
 * Version: 1.0
 */
/**
 * Make assigned coupon invalid if customer is an affiliate.
 */
function affwp_custom_block_affiliate_coupon_if_customer_affiliate( $condition, $coupon, $vars ) {
    
    if ( ! function_exists( 'affiliate_wp' ) ) {
        return $condition; // Make sure AffiliateWP is installed, otherwise just return.
    }
    $current_user_id = get_current_user_id();
    
    if ( empty( $current_user_id ) ) {
        return $condition; // Probably not logged in, just return.
    }
    if ( ! affwp_is_affiliate( $current_user_id ) ) {
        return $condition; // Not an affiliate, just return.    
    }
    
    if ( empty( $coupon->id ) ) {
        $coupon = affwp_get_coupon( $coupon->code );
// Add IF statement here that if the coupon code begins with 'affiliate-credit' return true to allow store credit coupons.
        if ( false !== $coupon && affwp_get_affiliate_user_id( $coupon->affiliate_id ) === $current_user_id ) {
            return false; // Dynamic coupon assigned to this affiliate, disallow the coupon.
        }
    }
    $is_tracked_coupon = get_post_meta( $coupon->id, 'affwp_discount_affiliate', true );
    if ( affwp_get_affiliate_user_id( $is_tracked_coupon ) === $current_user_id ) {
        return false; // Coupon assigned to this affiliate, disallow the coupon.
    }
    return $condition;
}
add_filter( 'woocommerce_coupon_is_valid', 'affwp_custom_block_affiliate_coupon_if_customer_affiliate', 10, 3 );

To give you some more info about what this code snippet does:

• This code snippet blocks affiliates to use discount coupon codes for new clients themselves (because they already got a discount when registering)

What I'm trying to accomplish by adding that IF-statement:

• Add an exception to the code snippet so that coupons for which the coupon code starts with the text 'affiliate-credit' are not blocked (so an affiliate is allowed to use that coupon). I understood it should be a very easy line of code to write for a PHP developer but I didn't have much success until now since my PHP knowledge is very limited.
• An example output value of $coupon beginning with 'affiliate-credit' is for example 'affiliate-credit-202308151438_44'. It can also have other output values like 'coupon123' or 'DADJGDLFSL".

Thank you in advance!