The bus is provided by Tbus, which is a private one (operator).
You are given this little thin strip of paper by the VA staff at the counter, and supposed to show this to the driver for your free ride.
As your next flight is a VAd, just drop by the VA counter, and show your next flight details, or QR coded BP if you have done OLCI.
The Tbus driver couldn't care, as its a free service provided by Sydney Airport.
Too many people for the bus driver to collect the small tear off slips.
Are you planning to drop off bags, for them to carry your plane hold luggage, or are you HLO.
The last time I was going from T1 to T2 with VA, the line was so long, every one who couldn't use the QFF side, was using the Tbus which is the free service.
I am HLO, so didn't want to wait for the free for all, so used the Sydney buses T1 to T2/T3 and paid with opal instead.
VA has some int flights coming in from NZ and Fiji, so the VA transfer desk at T1 should be staffed.
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Form the VA website, shouldn't have changed majorly:
Sydney
Sydney: International to Domestic
On arrival of your international flight, you are required to collect your bags from the carousel and clear Customs and Quarantine.
Once you have cleared Customs and Quarantine, follow the signs to the Virgin Australia transfer desk, located in the Arrivals Hall. The transfer desk will check you in for your domestic flight and accept your baggage. You can then follow the marked signs to the T-Bus pickup location for your connection to the domestic terminal. The T-Bus pickup location is located opposite exit A