There are NO documents that need to be uploaded for CY. You can upload your vaccination certificate, but it is not required. You should be able to OLCI with or without uploading.

Note that today ALL arrivals from the UK to LCA were being bussed to the bowels of the terminal building for mandatory PCR tests for all, without exception, then bussed back to the immigration area. Add 30-60 minutes to the arrival process and the risk of a positive test and mandatory quarantine in this event. Note first off the plane may mean last off the bus to a long queue for testing!

I did the test on arrival today off the BA664 at 1330 and got the (negative) result by text at 1700.