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This wikiHow will show you how to manually connect PayPal to Squarespace if your PayPal Business account is set up in Australia, Brazil, India, Israel, or Japan. If you're not located in these locations, you can simply log into your Squarespace website, click Commerce > Payments and select Connect PayPal.^[1]

[Edit]Steps

[Edit]Giving Squarespace API Permissions

Go to http://www.paypal.com/ and log into your business account. You'll need to log into your PayPal Business account. If you have a personal account, you can upgrade it for free.
Hover over your name and click . You'll see your profile name in the top right corner of the page. If you're signed into a personal account, you'll see a gear icon instead.
Click next to "API access." It's in the "Account access" tab, which should be active by default when you click Account Settings.
Click . This is under "Pre-built payment solution" near the center of the page and will allow 3rd-party platforms, like Squarespace, to access PayPal.
Enter "paypal-payments_api1.squarespace.com" next to "Third Party Permission Username" and click . This will give you the permissions needed for Squarespace to connect to your PayPal account.
Click to select all the boxes and click . After this step is done, you'll have successfully granted API permissions from PayPal to Squarespace.

[Edit]Copying Your PayPal Merchant ID

Go to http://www.paypal.com/ and log into your business account. You'll need to log into your PayPal Business account. If you have a personal account, you can upgrade it for free.
Hover over your name and click . You'll see your profile name in the top right corner of the page. If you're signed into a personal account, you'll see a gear icon instead.
Click . It's in the vertical menu on the left side of the screen under the header, "Business Profile."
Copy the information next to "PayPal Merchant ID." To copy this information easily, select the text and press Ctrl + C (Windows) or Cmd + C (Mac). You'll be pasting this information later.

[Edit]Connecting to PayPal

Log into your Squarespace site. You'll need the PayPal Merchant ID you copied earlier.
Click . It's in the "Home Menu" on the left side of the page.
Click . The list of payments for your website will display.
Click and enter your PayPal login information. Once you've entered your login information, you will see a text field for your merchant ID.
Paste the PayPal Merchant ID. To paste, click your cursor in the text field and press Ctrl + V (Windows) or Cmd + V (Mac).
Click . Customers will now be able to pay with PayPal on your site.^[2]