Copy field value to a new field in existing index - elasticsearch

Question

I have a document that has the structure with an field object with a nested field internally. The nested field is responsible for storing all interactions that occurred in an internal communication.
It happens that I need to create a new field inside the nested field, with a new type that will now be used to store the old field with a new parser.
How can I copy the data from the old field to the new field inside the nested field?
My document:
curl -XPUT 'localhost:9200/problems?pretty' -H 'Content-Type: application/json' -d '
{
"settings": {
"number_of_shards": 1
},
"mappings": {
"problem": {
"properties": {
"problemid": {
"type": "long"
},
"subject": {
"type": "text",
"index": true
},
"usermessage": {
"type": "object",
"properties": {
"content": {
"type": "nested",
"properties": {
"messageid": {
"type": "long",
"index": true
},
"message": {
"type": "text",
"index": true
}
}
}
}
}
}
}
}
}'
My New Field:
curl -XPUT 'localhost:9200/problems/_mapping/problem?pretty' -H 'Content-Type: application/json' -d '
{
"properties": {
"usermessage": {
"type": "object",
"properties": {
"content": {
"type": "nested",
"properties": {
"message_accents" : {
"type" : "text",
"analyzer" : "ignoreaccents"
}
}
}
}
}
}
}
'
Data Example:
{
"problemid": 1,
"subject": "Test",
"usermessage": [
{
"messageid": 1
"message": "Hello"
},
{
"messageid": 2
"message": "Its me"
},
]
}'
My script to copy fields:
curl -XPOST 'localhost:9200/problems/_update_by_query' -H 'Content-Type: application/json' -d '
{
"query": {
"match_all": {
}
},
"script": "ctx._source.usermessage.content.message_accents = ctx._source.usermessage.content.message"
}'
I tried the code below but it didn't work, it returns an error.
curl -XPOST 'localhost:9200/problems/_update_by_query' -H 'Content-Type: application/json' -d '
{
"query": {
"match_all": {
}
},
"script": "ctx._source.usermessage.content.each { elm -> elm.message_accents = elm.message }"
}
'
Error:
"script":"ctx._source.usermessage.content.each { elm -> elm.message_accents = elm.message }","lang":"painless","caused_by":{"type":"illegal_argument_exception","reason":"unexpected token ['{'] was expecting one of [{, ';'}]."}},"status":500}%