IRS Notice CP163 is a "reminder" notice of taxes due, usually Employer Business Taxes for Form 941 withholding. It is essentially the same letter as Notice CP160 & CP187 and the Collection reminder letters sent to individuals.
Respond to Notice CP163
The IRS has probably already sent a Notice of Intent to Levy (CP504B) so they could seize the business property at any time. But, these reminder notices indicate that the IRS is not actively seeking enforced collection immediately. You have a little time to address the problem.
The Form 941 taxes are not dischargeable in bankruptcy and the IRS will likely assess the tax against the owners of the business or anyone responsible for paying the taxes so the IRS has 2 avenues of collection available.
It will be important to investigate the nature & source of this liability. If it can be reduced, the forms must be prepared. If it cannot be reduced financial information will have to be provided. Most likely, the Account Transcripts will have to be ordered & compared with the company records.