[A] If your screen look like below and you are unable to integrate Purchase Invoices please follow below steps.
 

[B] Click "ctrl" + "-" from your keyword until the purchase voucher option appear or

click on three dot option available on upper right corner of the browser.

[C] Click "-" available besides Zoom until the purchase voucher option appear 

Keywords - Can not flow purchase invoice, purchase invoice option not available in extension

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