Cannot import Bitwarden vault.

I am new to 1Password and am attempting to import vault Data from Bitwarden to 1Password.  The instructions have been followed to the letter but each time I get the same error.

"Your import failed  1Password couldn't import the data.  The file maybe of the wrong format."

I have also tried using encrypted json files and get the same error.  The json file has been checked using a json validator.

Can anyone advise me what I could be doing wrong please?  Thanks.