I realise there are two or three previous threads on this but I've (carefully) applied their advice and it's still not working 
I'm automating creating a new ticket when a ticket changes workflow status. I want to copy across a custom field with a numeric value to the new ticket. Here's the code I'm using:
{
"fields": {
"parent": {"id": "28996"},
"customfield_10413":"{{issue.customfield_10413}}"
}
}
(The "parent" setting is irrelevant but included just so you can see the full code)
In the automation logging, I get the following error:
Create issue
Error creating issue
Specify a number for the custom field (below 100,000,000,000,000) (customfield_10413)
In the names page for the ticket, the custom field value appears as follows:
"customfield_10413":4.0
Can anyone advise please?