Under a Credit Support Annex (CSA), a margin call is only made if the required collateral transfer amount is greater than or equal to the Minimum Transfer Amount (MTA).

First, let's look at the initial state:

• Exposure = CNY 25,000,000
• Threshold = CNY 14,000,000
• Uncollateralized Exposure Limit = Exposure - Threshold = CNY 11,000,000
• Collateral Posted = CNY 10,800,000
• Collateral Deficit = CNY 11,000,000 - CNY 10,800,000 = CNY 200,000 Since the deficit (CNY 200,000) was below the Minimum Transfer Amount (CNY 2,500,000), no collateral transfer was required.

Now, for the new state:

• New Exposure = CNY 27,000,000
• Threshold = CNY 14,000,000
• Required Collateral (above threshold) = CNY 27,000,000 - CNY 14,000,000 = CNY 13,000,000
• Current Collateral Posted = CNY 10,800,000
• New Collateral Deficit = CNY 13,000,000 - CNY 10,800,000 = CNY 2,200,000

Because the new collateral deficit of CNY 2,200,000 is still strictly less than the Minimum Transfer Amount of CNY 2,500,000, a margin call will not be triggered. Therefore, the additional collateral required to be posted is CNY 0.