"Cannot read property 'getAddressString' of null" error

After the first try where i connected the wallet, and it charged me I think around $15 to create the account, which worked, it got to the minting part, which failed due to insufficient funds, which it does not tell you how much is needed. Then I’ve added more funds but now I get this error:

I have tried reconnecting and even recreating the collection from scratch but I still get this error. (I’m using MEW wallet)

Any idea why it errors and how to solve it?

Also, what are the minting cost? a single transaction’s gas cost? It would be nice if it said so somewhere.

Thanks in advance.