How do I include PST(British Columbia) on purcahses (Materials) that are a billable expense,but only collect GST on Sales.

Hello, 

A billable expense is an expense you incur on your customer’s behalf when you perform a work for them. You can easily record and track billable expenses so your customer can reimburse them when they receive their invoice. I'd be happy to explain how you can add tax (PST) to your billable expense, and collect GST on sales. 

Follow this article for steps on how to enter a billable expense in QuickBooks Online: Enter billable expenses. As explained in the section called "Enter a billable expense", you can select the tax checkbox or choose a tax agency if you want to charge tax. PST you pay on expenses does not get deducted from those amounts when you file your PST. Due to this, PST is now included in the expense total or capital item you've purchased.

For information about how to add GST to your sales transactions, take a look at this article: Sales Tax overview. 

I hope this helps get you back on track. Let me know if you've got any other questions. 

Have a nice day.