Unexpected token '<', "<br /> <b>"... is not valid JSON

[techno]

Stai passando HTML invece di JSON.

Controlla il codice.

non mi sembra:

$dataFields = [
    "Artist" => $artist,
    "Track" => $track,
    "Cover" => $cover,
    "Program" => $nome_programma,
    "Speaker" => $speaker,
    "ImageProgram" => $image_program,
    "HourProgram" => $ora_programma,
    "ProgramNext" => $nome_program_next,
    "SpeakerNext" => $speaker_next,
    "ImageProgramNext" => $image_program_next,
    "HourProgramNext" => $ora_programma_next,
    "LiveStream" => $live_stream
];

echo json_encode($dataFields);