Anita
Hi 🙌,
there is no main or secondary cards at bunq (might be you use it more often and for you is the primary card).
Maestro is a Debit Master Card enabled for the Maestro circuit which is owned by MasterCard and it is mainly used in The Netherlands and Belgium (but works globally where MasterCard is accepted) ... it is usually not accepted for on line transaction as the system is quite old and can not be upgraded to modern on line shopping.
Maestro cards are not accepted by PayPal.. it is not even possible to add them to your wallet in the App so it is not possible that payments are rejected.
Cheers 🌈
GG