 geo_point field does not support GeoJson which can be a PITA if your data is in such a format. Indexing it as a geo_shape is an option but very wasteful.
server/src/test/java/org/elasticsearch/index/search/geo/GeoPointParsingTests.java
try (XContentParser parser2 = createParser(JsonXContent.jsonXContent, BytesReference.bytes(content))) {
            parser2.nextToken();
            Exception e = expectThrows(ElasticsearchParseException.class, () -> GeoUtils.parseGeoPoint(toObject(parser2), randomBoolean()));
            assertThat(e.getMessage(), is("field must be either lat/lon or geohash"));
        }
    }
    public void testInvalidField() throws IOException {
        XContentBuilder content = JsonXContent.contentBuilder();
        content.startObject();
        content.field("lon", 0).field("lat", 0).field("test", 0);
        content.endObject();
        try (XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(content))) {
            parser.nextToken();
            Exception e = expectThrows(ElasticsearchParseException.class, () -> GeoUtils.parseGeoPoint(parser));
            assertThat(e.getMessage(), is("field must be either [lat], [lon] or [geohash]"));
        }
        try (XContentParser parser2 = createParser(JsonXContent.jsonXContent, BytesReference.bytes(content))) {
            parser2.nextToken();
            Exception e = expectThrows(ElasticsearchParseException.class, () -> GeoUtils.parseGeoPoint(toObject(parser2), randomBoolean()));
            assertThat(e.getMessage(), is("field must be either [lat], [lon] or [geohash]"));
        }
    }
    public void testInvalidGeoHash() throws IOException {
        XContentBuilder content = JsonXContent.contentBuilder();
        content.startObject();
        content.field("geohash", "!!!!");
        content.endObject();
        try (XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(content))) {
            parser.nextToken();
            Exception e = expectThrows(ElasticsearchParseException.class, () -> GeoUtils.parseGeoPoint(parser));