graphql 4.x retrieving paragraph fields

I've been attempting to retrieve paragraph fields from a node, and could really do with a solid working example. Ive tried following https://github.com/drupal-graphql/graphql/pull/968
But am getting an error.
So my example:
node called Event
->entity_reference_revisions called field_venue_type pointing at 2 Paragraph types
-> Paragraph -> virtual_meeting
-> physical_meeting

My Schema

type Business_Event {
id: Int!
venueType: [VenueType]
}
interface VenueType {
id: Int!
}
type VirtualMeeting implements VenueType {
id: Int!
}
type PhysicalMeeting implements VenueType {
id: Int!
placeName: String
}

My Resolvers

$registry->addFieldResolver('Business_Event', 'venueType',
$builder->produce('entity_reference_revisions')
->map('entity', $builder->fromParent())
->map('field', $builder->fromValue('field_venue_type'))
);
$registry->addTypeResolver('VenueType', function ($value) {
if ($value instanceof Paragraph) {
switch ($value->bundle()) {
case 'physical_meeting': return 'PhysicalMeeting';
case 'virtual_meeting': return 'VirtualMeeting';
}
}
throw new Error('Could not resolve VenueType type.');
});
$venueItemBuilder = $builder->compose(
$builder->produce('entity_reference_revisions')
->map('entity', $builder->fromParent())
->map('field', $builder->fromValue('field_venue_type'))
);
$registry->addFieldResolver('PhysicalMeeting', 'id',
$builder->compose(
$venueItemBuilder,
$builder->produce('entity_id')
->map('entity', $builder->fromParent())
)
);
$registry->addFieldResolver('PhysicalMeeting', 'placeName',
$builder->produce('property_path')
->map('type', $builder->fromValue('entity:paragraph'))
->map('value', $builder->fromParent())
->map('path', $builder->fromValue('field_place_name.value'))
);
$registry->addFieldResolver('VirtualMeeting', 'id',
$builder->produce('entity_id')
->map('entity', $builder->fromParent())
);

These all appear as expected in the explorer, but when i run the query

query MyQuery {
business_event(id: 909) {
venueType {
id
... on VirtualMeeting {
id
}
... on PhysicalMeeting {
id
placeName
}
}
id
}
}

I only get

{
"data": {
"business_event": {
"venueType": [
null
],
"id": 909
}
},
"extensions": [
{
"message": "Class 'Drupal\\businesslisting_graphql\\Plugin\\GraphQL\\Schema\\Error' not found",
"locations": [
{
"line": 3,
"column": 5
}
],
"path": [
"business_event",
"venueType",
0
]
}
]
}

Any pointers you might be able to give me to solve this gratefully received, hoping its something simple, rather than an issue with your excellent module. Many thanks