From tomorrow, fares will be payable again on some London buses. From
TfL's weekly newsletter:

From Saturday 23 May, we ask all customers using buses that only have
a front set of doors to start touching in again when they board.
Please follow the signs on the bus. These routes include: 124, 138,
146, 162, 192, 233, 273, 315, 318, 322, 336, 352, 354, 356, 367, 377,
379, 383, 385, 394, 404, 424, 434, 462, 463, 464, 481, 631, B13, B14,
E5, E10, E11, G1, H2, H3, H20, H26, K1, K4, K5, R1, R3, R4, R5, R6,
R7, R8, R10, S3, S4, U9, W4, W5 and W12.

Additionally, all passengers using the following New Routemaster bus
services, should continue to board via the middle doors and touch in
at the middle doors: 3, 9, 11, 12, 15, 19, 21, 24, 27, 38, 59, 67, 68,
73, 76, 87, 137, 148, 149, 159, 211, 253, 254, 415, 453, EL1, EL2 and
EL3. Single-decker routes 507 and 521 will also return to taking
contactless and Oyster payments but will continue to use middle door
boarding.