How can I full refund or partial refund paid invoice using PHP SDK ?

Let me share details about how QuickBooks Online (QBO) handles your customer refunds, ashish2020.

You can create a Refund receipt to process either a full or partial refund to your customer's paid invoice. However, doing it by using PHP SDK isn't currently possible in QBO.

To recommend the option to refund customers using PHP SDK, I'd suggest visiting our Intuit Developers page. 

This is where developers engage with others to discuss programming concerns. You can post your question from there. This way, our developers can provide you an accurate resolution about creating a refund using PHP SDK. I'll guide you how. 

1. Go to this link: https://help.developer.intuit.com/s/.
2. Choose QuickBooks Online under What do you need help with?. 
3. Click Ask a Question. 
4. Log into your existing Intuit Developer Account or create a new one. 
5. Enter your concern. 
6. Click Ask. 

I've attached screenshots below that shows the first to fourth steps.

Additionally, you can always utilize the API Docs & Tools menu on the Intuit Developer's page. From there, you can access the SDKs menu to guide you on how to possibly execute the said process in QuickBooks.

Please let me know if you have other concerns. I'm just around to help.