It is FDA cleared rather than approved, which is a lower bar. And it appears to be cleared as a tanning device, not as a Vitamin D-related device:

https://www.accessdata.fda.gov/cdrh_docs/pdf15/K151721.pdf

Note that the manufacturer has gotten in trouble with the FDA before:

https://www.fdalabelcompliance.com/letters/ucm284022

So I'd maintain some skepticism on the product's efficacy as it related to health. (I tried finding other clearances related to the product and failed, but they might still be out there...)