Thank You
The gates will let you through as long as there is still money on the card, but the top-up won't be added until you enter or leave at the station you selected. When you go through the gates there, your top-up will be added.
The way it works is that the stations aren't connected to the central computer all the time. When you top up online, that goes on to the central computer, but it won't be transmitted to your selected station until the tube closes for the night and they do the big overnight update. THEN the computer and all the stations "talk" to each other and your top-up gets sent to your selected station. So you can only get it next day, and only from the station you selected. So it just makes sense to always select the station you're most likely to use next, and now you know WHY you have to select a station!
And if you don't "collect" your top-up within a week, it will be returned. Personally I find it easiest to just use a ticket machine next time I travel.
If you want to collect that top up you have to go to where you sent it to collect it. That is the only way that top up will go on the card.
In terms of "letting you through the gates" it will depend if you have any money on the card, not including the top up you mention.
There is no station called Oxford Street. It is Oxford Circus
The top up will only happen when you pass through your designated station.
just don't top up online. top up at the station your going through.
