CPO5 is the type of notice it is. Your return has been selected to be reviewed by the IRS. They review certain items on your return. There is usually no need to be concerned and it is often random selection. If they need further information, they will send you a letter asking for more details.
According the the following IRS webpage: https://www.irs.gov/Individuals/Understanding-Your-CP05-Notice Also, more details can be found at that link.
They sent you this notice because they're reviewing your tax return to verify:
- The income you reported on your return
- The income tax withholding amounts you reported on your return
- The claims for tax credits you made on your return
- The withholding claimed on your Social Security benefits
- The household help you claimed
- The Schedule C income you claimed
