Question: I have installed free price extension, <https://pluginarchive.com/magento/rp_display_price_free> the extension collapse my configurable product price. How to debug which part of the extension affects my Magento core function.

Note: <https://snipboard.io/I2FrSH.jpg>

Thanks in advance..!

Answer: 
Couple of points would like to add here that one can not easily render string (in this case its **FREE** - system config (`displayfreeprice/general/freeprice_text`) ) into the price format which may be float or decimal in most of the cases.

Although, one workaround should resolve this issue showing **0.00** instead of its value.

You can do as follows:

1. `Open <magento-root>\app\code\local\Rp\Displayfreeprice\Helper\Productprice.php`
2. Look for the function named
`public static function currency( $price , $format=true , $includeContainer = true )`
3. Find the below statement.

`return parent::formatPrice($price, $includeContainer);`

4. Replace it with below statement.

`return parent::currency($price, $includeContainer);`

Refresh the cache and session and then open configurable product page.

I guess extension vendor FORGOT to replace the function name.
I didn't work with Magento 1 for a long time. It's just my suggestion: We should have Debug tools.

* PHP: Xdebug and PHPStorm are perfect choices. <https://www.jetbrains.com/help/phpstorm/configuring-xdebug.html>
* Javascript: Developer Tool <https://developers.google.com/web/tools/chrome-devtools/javascript>

Price calculation flow is not easy.

Read more:

[Magento 1.9 - How to debug - Configurable product price changed to 0 if chooses colors attribute](https://magento.stackexchange.com/questions/291238/magento-1-9-how-to-debug-configurable-product-price-changed-to-0-if-chooses)

Will update more here.