`estimatefees` has changed in CLN version v23.05.

`estimatefees` has changed in CLN version v23.05.

See deprecated section in https://github.com/ElementsProject/lightning/blob/master/CHANGELOG.md#23051---2023-06-05-austin-texas-agreementatxa-ii.

The new spec is (https://github.com/ElementsProject/lightning/blob/master/doc/PLUGINS.md#estimatefees):

`estimatefees`

Polled by `lightningd` to get the current feerate, all values must be passed in sat/kVB.

The plugin must return `feerate_floor` (e.g. 1000 if mempool is
empty), and an array of 0 or more `feerates`. Each element of
`feerates` is an object with `blocks` and `feerate`, in
ascending-blocks order, for example:

```
{
"feerate_floor": ,
"feerates": {
{ "blocks": 2, "feerate": },
{ "blocks": 6, "feerate": },
{ "blocks": 12, "feerate": }
{ "blocks": 100, "feerate": }
}
}
```

lightningd will currently linearly interpolate to estimate between given blocks (it will not extrapolate, but use the min/max blocks values).