You need to make sure the layer.json at that urlpath is configured with an “availability” array. Unfortunately this functionality is not very well documented by the team but you see some of them discussing it here sampleTerrainMostDetailed problem - #7 by omar
An example of what mine looks like (note the settings are very specific to my map and may not work in your case). The below availability array is configured to load all tiles to z22.
{
"tilejson":"2.1.0",
"format":"quantized-mesh-1.0",
"scheme":"slippyMap",
"minzoom":0,
"maxzoom":22,
"available":[
[
{
"endX":1,
"endY":0,
"startX":0,
"startY":0
}
],
[
{
"endX":3,
"endY":1,
"startX":0,
"startY":0
}
],
[
{
"endX":7,
"endY":3,
"startX":0,
"startY":0
}
],
[
{
"endX":15,
"endY":7,
"startX":0,
"startY":0
}
],
[
{
"endX":31,
"endY":15,
"startX":0,
"startY":0
}
],
[
{
"endX":63,
"endY":31,
"startX":0,
"startY":0
}
],
[
{
"endX":127,
"endY":63,
"startX":0,
"startY":0
}
],
[
{
"endX":255,
"endY":127,
"startX":0,
"startY":0
}
],
[
{
"endX":511,
"endY":255,
"startX":0,
"startY":0
}
],
[
{
"endX":1023,
"endY":511,
"startX":0,
"startY":0
}
],
[
{
"endX":2047,
"endY":1023,
"startX":0,
"startY":0
}
],
[
{
"endX":4095,
"endY":2047,
"startX":0,
"startY":0
}
],
[
{
"endX":8191,
"endY":4095,
"startX":0,
"startY":0
}
],
[
{
"endX":16383,
"endY":8191,
"startX":0,
"startY":0
}
],
[
{
"endX":32767,
"endY":16383,
"startX":0,
"startY":0
}
],
[
{
"endX":65535,
"endY":32767,
"startX":0,
"startY":0
}
],
[
{
"endX":131071,
"endY":65535,
"startX":0,
"startY":0
}
],
[
{
"endX":262143,
"endY":131071,
"startX":0,
"startY":0
}
],
[
{
"endX":524287,
"endY":262143,
"startX":0,
"startY":0
}
],
[
{
"endX":1048575,
"endY":524287,
"startX":0,
"startY":0
}
],
[
{
"endX":2097151,
"endY":1048575,
"startX":0,
"startY":0
}
],
[
{
"endX":4194303,
"endY":2097151,
"startX":0,
"startY":0
}
],
[
{
"endX":8388607,
"endY":4194303,
"startX":0,
"startY":0
}
]
],
"tiles":[
"/{z}/{x}/{y}.terrain"
],
"extensions":[
"octvertexnormals"
]
}