Is it wise to contribute such a (relatively) high amount into my monthly RSP for STI ETF every month, especially when it's making a loss?

Like what the rest has mentioned. It’s too risky to just invest in STI ETF only. You need some global exposure, you can consider IWDA(+EIMI for the emerging markets exposure) or VWRD or VWRA.

Reduce the STI ETF amount and buy into one or two of these ETFs. The ratio all depends on your risk appetite. You can read up more online before buying them.

Hey there, in my opinion, I would still put some money into STI ETF for local exposure because I would still eventually retire in Singapore so I would still believe that Singapore economy will be strong in the future (but who knows!). Nevertheless, I would still diversify by investing in overseas ETF such as those suggested by the ppl before me (e.g. S&P 500 ETF). I would personally go for global ETF with exposure to developed countries economy as they would provide the best diversification. One example is IWDA which I plan to invest in the future once I have the cash. So maybe if I were you, I would consider still putting 500 dollars into OCBC BCIP but I would choose to put the other 500 into IWDA for global exposure!

Importantly, you need to be stay invested for the long-term as markets can fluctuate so when you do DCA you can still eventually earn a profit overall. By long term I mean 20 to 30 years down the road till your retirement age.

This is just my two cents and there might be better advice and opinions out there! I'm still learning and I learnt greatly from this book called "Rich by Retirement" by Joshua Giresch. It's a great book and I hope you can find time to read it if possible!