My tax refund is aproved to be sent on the 18th of mach but today march 16th I got a CPO5 letter. What does this mean?

The CP05 notice means that the IRS is holding your refund until they can review and verify some of your information. See the link below for more information.

https://ttlc.intuit.com/community/refunds/help/i-got-a-cp05-notice-from-the-irs/00/27063