IBAN is the international bank number.

For donations they also offer liberapay so you can use stripe and PayPal.

For membership fees you can also use direct bank transfer.

You can make SWIFT transactions to IBAN numbers. no problem whatsoever.

SEPA is essentially just a specific subset service set of a SWIFT international bank transfer. Or in other words, the interface of SEPA is a subset of parameters in SWIFT transfer. And it mandated IBAN numbers on stragglers in EU.