Thats right, 2023 slips filing is not available yet in Profile due to CRA changes this year, it will be available in R3.0 next week.

If you are submitting the XML through CRA's "Represent a Client", enter your RepId  and enter the transmitter number (BN). Not entering a BN might be acceptable too but this would have to be confirmed with CRA.

The business number depends of the types of slips, for T4, T4A  RP, T5 RZ etc.