Here's a report from another site... refusal to board
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Here is a first hand story. Myself and girlfriend were going to POP this past May. You could do the e-ticket, known as a QR code, or you could get the paper immigration form on the plane of when you land from immigration personnel. We went to check in with American that morning and were refused boarding because we did not have the QR code, and agent did not know the rules. Missed flight, huge mess with plans, lots of extra time and money spent, letters to American Airlines, etc. Went two days later to STI, without the help of American Airlines, thank you very much. Best to just do the QR code prior to leaving, and there is also another one for departing the DR, but they don't really look at the departure one much.