Yes, of course, there is scope for negotiation. You can add a message to your bid while publishing it. You can also initiate a conversation confirming the actual price of the bid. This chat/conversation can be held privately with the employer.
My card got charged however, the work hasn’t been started? May I know why?
The amount gets deducted when you accept a bid. You will be redirected to a checkout page from where the payment will be done to