What should be done after informing the flight deck when using portable oxygen?

When using portable oxygen, it's crucial to ensure that the oxygen flow is functioning correctly. After informing the flight deck, checking the oxygen flow in the hatbin is essential to verify that the portable oxygen equipment is operating as intended. This step is particularly important for maintaining the safety and well-being of the passenger who requires supplemental oxygen during the flight.

Ensuring proper oxygen flow helps to prevent any potential complications that could arise from insufficient oxygen supply, particularly at high altitudes where oxygen levels are lower. This check acts as a confirmation that the equipment is not only available but also operational, which is critical for the passenger's health and safety during the flight.

Other actions such as turning off the oxygen, seating the passenger upright, or removing makeup may not directly pertain to the immediate task of ensuring the oxygen supply is adequate for the passenger’s needs in this scenario.