To upload purchase invoices document in CStore Essentials use the following steps:
Login to your Essentials Account
Click on Grocery -> Purchases -> Invoices (Note: you can also get to invoices from Pricebook > Purchasing > Invoices)
Click on the "+" button on the top right to add a new invoice
Enter the invoice date, vendor name, payment details, Purchase amount, invoice number (optional) and click on Add Invoice.
Note: If you are paying by cash, either select pending/unpaid and pay from day report later or enter purchase in the day report.
After the invoice is added, click on the Paper Clip to attach an invoice. Drag and drop the file or click in the blue box to select the file.