Solution to:

"Error: We are unable to process your submission because the transmitter CRA account number given in the attached T619 electronic transmittal record does not match the account number you used to sign in."

If filing Client T4s through Represent a Client:

1. go into EFILE / Options / T3/FX / Transmitter, and

2. change Business Number to your Client's CRA Business Number ending in RP000X.

This is prepopulated with your own Business Number and must be changed to your Client's Business Number (in this case, their Payroll number).