Bougainvillea flowering problem
bougainvillea is a qualitative short day plant meaning that it needs long, uninterrupted nights to flower. Most flowring accours when it gets 8hrs of light (=16 hrs of night).
India is a huge country so you need to be more specific or tell us how many hours of light the plant gets. Note that if it's exposed to light from the house/street it may not flower as the light intensity for photoperiod is much smaller than that of photosynthesys.
Flowering requires a lot of energy, even if all conditions are met not enough sunlight might prevent flowering. bougainvillea loves sun, give it as much direct light as possible.
According to fao, Paclobutrazol shortens the time to flowering in long day conditions, meaning that GA might delay flowering. Another way to prevent GA synthesis is to stop watering the plant. Once the leaf start to fall give it water again.
Don't water too much:

these plants need full sun &amp; well-drained soils. After establishing,
minimal watering is needed. Two or more irrigations with 3/4 – 1″ of
water per week would provide too much water for the bougainvillea to
bloom well.

What to do:

Give it more sun
Give it less water
Induce water stress to prevent GA synthesis
shorten the day, you may cover the plant with a dark cloth from the late afternoon to the morning