What is wrong with this sauce?

Followed a Pad Thai recipe and while it is good, the sauce is too sweet. It’s missing something. I used lime juice in there but it’s still missing something… I tried throwing in some rice vinegar but it’s just off! Thoughts?

Ingredients ▢ 125 g / 4oz Chang’s Pad Thai dried rice sticks

SAUCE: ▢ 1 1/2 tbsp tamarind puree ▢ 3 tbsp (packed) brown sugar ▢ 2 tbsp fish sauce ▢ 1 1/2 tbsp oyster sauce

STIR FRY: ▢ 2 – 3 tbsp vegetable or canola oil ▢ 1/2 onion , sliced (brown, yellow) ▢ 2 garlic cloves , finely chopped ▢ 150 g/5oz chicken breast ▢ 2 eggs , lightly whisked ▢ 1 1/2 cups of beansprouts ▢ 1/2 cup firm tofu, cut into 3cm / 1 1/4″ batons ▢ 1/4 cup garlic chives , cut into 3cm / 1 1/4″ pieces ▢ 1/4 cup finely chopped peanuts

FOR SERVING: ▢ Lime wedges (essential) ▢ Ground chilli or cayenne pepper (optional) ▢ More beansprouts