Add the cron "PayPal: Process invoices for recurring payments". This ensures that PayPal transactions are regularly matched with your (unpaid) invoices for recurring payments.
My invoices are never set to "paid"
Check your error log
You may see warnings about "Unclaimed" PayPal transactions. This means that the currency of the transaction does not match the currencies currently set up in your merchant account. Please see the notes above to see how to add currencies.
You may then click on the transactions in your PayPal dashboard and manually accept them afterwards. If this is done they are parsed in QUIQQER (upon next cron execution) and matched to your invoices.