A 1003 error means your client has locked their online banking access. This could be for a number of different reasons i.e. from too many incorrect login attempts or running out of time to input a verification code/token.

Your client will need to go to their banks' website and go through their standard password reset process. Once the correct login details are in order, your client can return to the link you sent to re-add their bank.

Example below. If your client selects a bank and provides the incorrect login details.

They will see an error message advising that the incorrect credentials have been provided.

If your client attempts to use the incorrect login details too many times, their online banking access will be locked by the bank, and it can only be reset via the bank's online banking portal.