How to add purchases tax?

Hello, rola alluhaydan. 

We need to ensure to set up the sales tax first: I'll show you how to do it: 

1. Click Taxes, and choose Sales Tax. 
2. Tap Set up tax. 
3. Set up the necessary details ,then select Next.
4. Follow the steps to finish and select Done.

You'll see a Tax/GST column on your sales and purchases forms. To learn more about GST/VAt rate, you can check out this article: How do I set up sales GST/VAT rates and use them on forms?  

I'd also recommend consulting with your accountant or a tax expert for additional guidance in properly recording tax in QBO.

For more details applying sales tax to the transaction, refer to this article: Applying Sales Tax to Transactions and Sales Forms. 

Please reply to this post by adding some details below if you need anything else with Sales Tax. I'm here to help. Stay safe!