MooMoo prompted that the transaction is a margin with the following highlight "If buying will use margin" but i have sufficient cash in my account.

Check if you have the USD margin account have the exchanged currency amount needed. Suspect that the SGD or HKD deposited account, you need to made an currency exchange.

What option stratergy are u using? Credit stratergies usually block margin > debit. Blocking margin buying power doesn’t mean you will be charged margin loan. It just means money will be frozen for purposes of assurance you can pay in the event the trade goes against you.

Certain Specific terms may be unique to your broker so you might want to check with them what they mean if you can’t find similar terms online