404 on sendConfirmationEmail

When I try to send a confirmation email using the link on mailpoet subscribers list, I can see a 404 error on the console.

The data sent is ({token} was a token):

action: mailpoet
api_version: v1
token: {token}
endpoint: subscribers
method: sendConfirmationEmail
data[id]: 34

And response is:
{“errors”:[{“error”:”unknown”,”message”:”An unexpected error occurred.”}]}

Other operations work properly.