Using legit regular banks would be your best bet to avoid scams or being accused of fiscal crimes.

It depends on where the billionaire’s and your bank account are located (some restrictions may apply), but a normal bank transfer works perfectly for any amount. Of course for large amounts it’s better to contact the banks first because it may reject a large deposit if it comes out of the blue.

For donations there will be taxes and some bureaucracy, the anti money laundering will be triggered, but it’s nothing impossible to handle.