After purchasing the ProductPress plugin, these are the steps to install the plugin, select your chosen Merchant of Record, and then connect the WordPress site with that provider.
1. CHANGE YOUR PERMALINK SETTINGS
Go to Settings > Permalinks. Choose the Post name setting, and click Save Changes.
2. INSTALL AND ENABLE THE PLUGIN
Go to the Plugins menu. Click Add New and then choose the Upload Plugin option at the top of the screen. Upload the ProductPress plugin zip file that you downloaded from your ProductPress licensing account.
Once installed, choose Activate plugin.
3. CHOOSE YOUR MERCHANT OF RECORD
Now, go to Settings > ProductPress. You’ll options for Paddle or Gumroad.
Select which provider you would like to use with the plugin, and click "Save Changes".
From here, follow the steps for "Setting up with Gumroad" or "Setting up with Paddle".