Backing up issue

what am I doing wrong?

> user@user-VAW70 ~ $ zcashd -exportdir=/home/user --daemon

Zcash server starting
user@user-VAW70 ~ $ zcash-cli backupwallet my_backed_up_wallet.dat
error code: -28
error message:
Loading block index...
user@user-VAW70 ~ $

OK looks like I just needed to run the daemon a while longer until the block info had downloaded more. However then it gave me:

error code: -4
error message:
Filename is invalid as only alphanumeric characters are allowed. Try 'mybackedupwalletdat' instead.

So I finally renamed as suggested and it worked. Is there any easy way to verify the validity of the backed up wallet file? I assume would need to rename it back to wallet.dat to later restore the backup.

Yep. To check validity, you can move out your existing wallet.dat and moving in the backup (renamed to wallet.dat) or running a separate instance with the backup. Or you can compare the two files if there haven't been any new transactions related to wallet with diff command.

So I did this (stopped zcashd, deleted old wallet.dat and restored from backup and restart zcashd) but trying to verify I got error code -28 for many minutes before it seemed to work. Is this correct behavior?

And still the restored wallet fails:

$ zcash-cli listreceivedaddresses
error code: -32601
error message:
Method not found

If I am just using one address at the moment, would it be easier to just use z_exportkey?

I'm still stuck here - anyone?