Retrieve the PDF document for a specific invoice by its ID
curl --request GET \
--url https://api.cloud.flexprice.io/v1/invoices/{id}/pdf \
--header 'x-api-key: <api-key>'"<string>"curl --request GET \
--url https://api.cloud.flexprice.io/v1/invoices/{id}/pdf \
--header 'x-api-key: <api-key>'"<string>"