I've been trying some variations which results in different errors like "Specify a number for the custom field (below 100,000,000,000,000)". Worth noting is that I'm doing this in Product Discovery.
{
"fields": {
"customfield_10324" : [{ "value" : "true"}]
}
}
{
"fields": {
"customfield_10324" : "true"
}
}