If i back up my wallet using multibit, can i open it with bitcoin core? I tested to back up my multibit but when i opened mybackup.wallet to my bitcoin core wallet, It showed "Payment request fetch URL is invalid." What was my mistake?
Bitcoin Core and MultiBit do not use the same wallet format. You can send bitcoins from one wallet to the other, and you may be able to export private keys from one and import them into the other, but you cannot simply open the wallet file from one of them with the other one.