I feel your pain. This is way more confusing than it needs to be, but presently it is still representative of the level of confusion that reigns with international travel. A "rt-PCR" test is considered to be the most sensitive of all of COVID-19 tests, with the 'rt' meaning 'reverse transcription.' I'm not going to delve into the details of this test, because it is explained on several websites in complete detail, but like any type of COVID-19 test it can fail to detect the virus is some situations. The PCR test is a type of rapid COVID-19 test that is typically just as accurate as the rt-PCR test, and is acceptable for entry back into the United States. As of 4/1/21, if traveling to St. Martin from the United States all you should need is a negative PCR test performed within 120 hours of your departure to SXM. Personally, I would avoid any place that does't now what a rt-PCR test is and suggest finding a place this week who can do the PCR test and get the results to you before you depart.