We had high hopes for this plugin but it's simply not up to the task when it comes to interfacing with PayPal if you want to control the PayPal experience at a level that PayPal permits. Especially when it comes to setting up donations. Our problem was to allow a client to make a donation by allocating amounts to various programs. Each amount needed to show on the PayPal receipt with an account code. Unfortunately the plugin only allows for one donation field, which seems terribly deficient.
Additionally, PayPal expects certain data types to be represented in certain ways or it ignores the data, especially with things like phone numbers. There are also some cart options that can't be specified and the first time we used the plugin to pull up our PayPal site we didn't recognize it because it was the stock issue and not the site we customized.
The solution we arrived at was to direct the POST data to a NON silent POST where we have the opportunity to reformat the entire POST to PayPal, which we then post after the document ready function fires and now we have our customized PayPal site working and all the payment fields are correctly pre-populated.
The downside is we had to forgo using the PayPal plugin altogether so we can't take advantage of the deferred e-mails. What we do instead is embed parameters in the Cancel and Return URLs we upload to PayPal that direct the browser back to the site where we can extract the GET values like "first_name" and "transaction id", etc. and display an acknowledgement for either a cancellation or a confirmation message. We can then execute code via a code insertion plugin to send e-mails and update the DB as necessary, etc. However, customers don't always return to your site in a predictable manner. They may "continue shopping" or not use the "return" button so the aforementioned procedure can't be relied on as payment confirmation. But in our case the accounting department doesn't rely on our backend data. They only go by the PayPal journal, which we seed with our transaction number (Ticket Component) as PayPal's invoice number, which is also one of the PayPal parameters the PayPal plugin does not accommodate. The accounting department can then query the DB by Transaction Number to get deeper donation data when they need it.
