Google Earth Engine: Error generating chart: Data column(s) for axis #0 cannot be of type string

Question

I'm trying to graph a time series of weather indices obtained from the Gridmet Drought product, but am getting the following error: Error generating graph: Data columns for axis #0 cannot be of type string.

This is my script:

var GRIDMET = ee.ImageCollection("GRIDMET/DROUGHT")
.filter(ee.Filter.date('2010-02-18', '2022-06-26'))
.filterBounds(PNI)
.select('spi30d','eddi30d','spei30d','pdsi','z');

print(GRIDMET);

var GRIDMET_2 = GRIDMET.map(function(image) {
  return image.set('timeFormat', image.date().format('dd-MM-yyyy'))});
  
print(GRIDMET_2);

var SPI = ui.Chart.image.seriesByRegion(
GRIDMET_2, PNI.geometry().bounds(), ee.Reducer.mean(), 'spi30d', 1000, 'timeFormat', 'label')
  .setChartType('ScatterChart')
  .setOptions({
    title: 'SPI a través del tiempo',
    hAxis: { title: 'Tiempo'},
    vAxis: {title: 'SPI'},
    lineWidth: 1});
   
print(SPI)

Answer 1

You don't provide access to your PNI variable so, I think your problem is in it. By using your code with an arbitrary PNI area in USA (with 2 features) as follows:

var geometry1 = ee.Geometry.Polygon(
        [[[-99.74885326262063, 41.2959303393308],
          [-99.74885326262063, 41.01468579876124],
          [-99.37531810637063, 41.01468579876124],
          [-99.37531810637063, 41.2959303393308]]], null, false),
    geometry2 = ee.Geometry.Polygon(
        [[[-98.77107005949563, 41.41138604975184],
          [-98.77107005949563, 41.02297491656624],
          [-98.24372630949563, 41.02297491656624],
          [-98.24372630949563, 41.41138604975184]]], null, false);

var PNI = ee.FeatureCollection([ee.Feature(geometry1, {label: 'area1'}), 
                                ee.Feature(geometry2, {label: 'area2'})]);

Map.centerObject(PNI, 9);

var GRIDMET = ee.ImageCollection("GRIDMET/DROUGHT")
.filter(ee.Filter.date('2010-02-18', '2022-06-26'))
.filterBounds(PNI)
.select('spi30d','eddi30d','spei30d','pdsi','z');

print(GRIDMET);

var GRIDMET_2 = GRIDMET.map(function(image) {
  return image.set('timeFormat', image.date().format('dd-MM-yyyy'))});
  
print(GRIDMET_2);

var SPI = ui.Chart.image.seriesByRegion(
  GRIDMET_2, PNI, ee.Reducer.mean(), 'spi30d', 1000, 'timeFormat', 'label')
  .setChartType('ScatterChart')
  .setOptions({
    title: 'SPI a través del tiempo',
    hAxis: { title: 'Tiempo'},
    vAxis: {title: 'SPI'},
    lineWidth: 1});
   
print(SPI)

the chart is produced without any problem; as it can be observed in following picture:

Complete code can also be accessed here.