You say "we" so I assume you are married filing jointly.
$4218 is an odd amount. That amount would require that you have two or more dependents, and adjusted gross income between $150,000 and $160,000. (Below $150,000 you would get the full amount of $1400 per person and above $160,000 you are ineligible, for married filing jointly.)
Start by viewing your online account, and checking to see how much the IRS thinks they paid to both you and your spouse. Also review any IRS letter 6475 that you or your wife received.
https://www.irs.gov/coronavirus/third-economic-impact-payment
If they IRS thinks they sent the full amount, but you received less, you can't get the difference on your tax return, you must trace the missing payment.