Press your lips together, add vocal cord vibration, then release.

Americans pronounce bonsai as BAHN-sahy (/ˈbɑnˌsaɪ/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "He creates bonsai trees as a relaxing hobby".
Record yourself saying "bonsai" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 5 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Press your lips together, add vocal cord vibration, then release.

Relax your lips and drop your jaw significantly. The tongue tip lightly touches behind the bottom front teeth and the back part of the tongue presses down a little to create more dark space in the back of the mouth.

Touch the tip or front edge of your tongue to the roof of your mouth behind your teeth. Air flows through your nose.

The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the first syllable, not the others. Stretch BAHN — keep everything else short and quick.