Customers may be charged tax twice
Turn EDD taxes off (Downloads → Settings → Taxes). Paddle calculates and collects tax itself. The plugin shows a reminder while EDD taxes are on.
The invoice link says “not available yet”
Paddle creates the invoice a moment after the payment. Try again in a minute.
A webhook arrived twice, or out of order
That is normal for Paddle, and the plugin is built for it: payments, renewals and refunds are never recorded twice. Developers can read how in Concurrency and idempotency.