On 10-16-20 we flew AA from DFW-MIA-SXM. Starting 24 hours prior to our flight We tried to check in online at aa.com. We tried several times on different computers, browsers and the aa app. All to no avail. Each time it told us we had to check in with an agent at the airport. A call to AA customer service yielded no answers. At the airport we were told it was due to the SXM travel requirements and they had to see our travel authorization and negative COVID-19 tests. Once reviewed we were issued boarding passes. We had a very tight connection in MIA that got tighter due to departing DFW 20 minutes late. The pilot made up 10 of those minutes. We were fortunate to land at gate 51 and depart at Gate 49. Upon arrival at Gate 49 they were already boarding. There were two lines. One line at the counter and another boarding. We entered the boarding line since our paperwork had already been checked. Wrong!!! We had to go back to the line at the counter and have our paperwork checked again before being allowed to board. It seemed redundant to have to have it checked both in Dallas and Miami. As others have said, our paperwork was checked again upon arrival before being allowed to go through immigration.