Creating a fulfillment service is returning an Internal Server Error

[gman007]

I'm trying to create a fulfillment service on a store like this: 

$data = array(
	"fulfillment_service" => array(
		"name" => "Example Name",
		"callback_url" => "https://www.example.com/",
		"inventory_management" => true,
		"tracking_support" => true,
		"requires_shipping_method" => true,
		"format" => "json"
	)
);
$url = 'https://'.$store_url.'/admin/api/2020-07/fulfillment_services.json?access_token='.$access_token;
$response = CustomRequests::postRequest($url, $data, $access_token);

It keeps returning {"errors":"Internal Server Error"} for this one particular store. It works for other stores. 
Any ideas why? 

The store has the write_fulfillments permission. 

x-request-id: bc7b0c0a-49ce-445c-bf40-59e2f8db89c4

Any help would be appreciated.