MapLibre uses XYZ by default (origin top-left, Y increases downward)
Some tile systems use TMS (origin bottom-left, Y increases upward)

For z=4, x=7, y=3:
  XYZ: y=3
  TMS (flipped): y=12

Let's test both:
curl 'https://tile.map.one/test_pm/tile.php?tile=raster.pmtiles&z=4&x=7&y=3'
curl 'https://tile.map.one/test_pm/tile.php?tile=raster.pmtiles&z=4&x=7&y=12'

If the second one returns a valid tile, we need to flip Y in tile.php