This is likely a CPC processing error, not an actual tax shortfall. Section 143(1) is an automated processing by the central processing centre and TDS mismatches are one of the most common causes of wrong demands.

Here is what to do immediately:

1. Download your Form 26AS and AIS from the income tax portal. Check if your TDS credits match what you declared in the ITR.

2. If TDS is in 26AS but NOT reflected in the 143(1) intimation: this is a CPC error. You can file a RECTIFICATION REQUEST under Section 154 on the e-filing portal. Go to Services > Rectification > Income Tax Return, select the relevant assessment year, and choose the correct basis (TDS mismatch).

3. If TDS is NOT in 26AS: the deductor (your employer or payer) has not filed their TDS return or has done so with an incorrect PAN. You need to contact the deductor to correct the TDS return. This takes time. While waiting, you can respond to the demand as DISAGREE with explanation.

4. Do NOT pay the demand blindly if you believe TDS was properly deducted and is in 26AS. Pay only the genuinely outstanding amount if any.

The RESPONSE DEADLINE for a 143(1) demand is within 30 days of the intimation date.

This [Section 143(1) intimation and demand response guide](https://taxgarden.in/blog/section-143-1-intimation-cpc-processing-demand-refund-india) covers the full process including rectification, grievance filing, and what each intimation type means.