Both phrases/sentences express same meanings
1: Sending json data to postgres once received from API

2: Sending json data to postgres after receiving from API

3:Sending json data to postgres once it's received from API

Question

Both phrases/sentences express same meanings
1: Sending json data to postgres once received from API

2: Sending json data to postgres after receiving from API

3:Sending json data to postgres once it's received from API

Answer

Yes, they all have the same meaning.
The 2nd phrase (if part of a sentence and not just a summary phrase) would read better if you replaced 'after receiving' with 'after receiving it'.

Evden çıkmadan dil öğrenme fırsatını kaçırmayın. Deneyimli dil eğitmenlerimizden oluşan seçkimize göz atın ve ilk dersinize şimdi kaydolun!