Beckton Park station, like those at that end of the DLR, is built underneath the grade-separated main road (A1020) so the bus stops are accessed by using the park-level walk to “Straight Road”. . Underneath the roundabout there is a bridge that connects the bus stops to sound side of the DLR.
The satellite view helpfully shows where the stops are actually located as they are marked in on the road. So the correct position for “X” is 51.50924197726067, 0.05475553212808522