This is for the transmitter number....
From this link https://www.canada.ca/en/revenue-agency/services/e-services/filing-information-returns-electronicall...
CRA explains that you can put all 0's
Account Number
- Required, 15 alphanumeric, 9 digits RZ 4 digits, example 000000000RZ0000
- must correspond to the Account number on the related T5018 Summary record.
- if you have not been notified of your number, or you are unsure of your number, contact our Business Enquiries line at 1-800-959-5525
- if you have not been able to obtain a BN RZ, enter 000000000RZ0000 in the field
Note: In order to process a return, the complete Account number is Required.
