I do a bit of volunteer work, and that organization has a free-tier WordPress website and a PayPal account.
They want to add an online sign-up feature to their website that includes collecting $10 dues.
Here's how to accomplish that without paying for any new products.
We will use a standard WordPress Form's "submit" button to launch a PayPal web page, and then tell PayPal the WordPress landing page to use after payment is complete.
First, create a Form.
Not a feedback box or anything fancy. Just a couple fields and a "Submit" button.
Next, select/highlight the Form so we can see the Properties.
Here's the meat of the changes to WordPress:
On Submission, we want to redirect to PayPal. We don't know that URL yet, we must get it from PayPal
Submission also generates an email. We must tell WordPress to whom that email should go and what it should be called.
Log into the organization PayPal (not your personal) and find the no-code link builder at https://www.paypal.com/buttons/smart/.
Build the $10 transaction here
Click "Build It!" It will return options for a button, a link, and a QR code.
The button requires javascript, so it won't work in the WordPress free tier.
The link is the redirect page that we seek for the WordPress form.
The QR code may have use if directed from some other sign-up method.
Next, let's tell PayPal where to redirect after the transaction is complete.
In PayPal, go into Account Settings, and select Website Payments, then select Website Preferences. Enter the landing page back in WordPress. (You might need to create one).