returnReasonCode deve ser um código do Banco Central — consulte via operationId consultarMotivosDevolucao.curl --location 'https://api-hml.lcpay.com.br/api/movimentacao/236BD098-F481-48D6-6F7F-A357E09DEB45/instant-payments/019f6b33-af9e-bacb-cbe3-4150267572ac/returns' \
--header 'Content-Type: application/json' \
--data '{
"externalIdentifier": "d81540e9-e579-4352-9b98-00552cb39164",
"amount": 50,
"returnReasonCode": "MD06"
}'{
"data": {
"transactionId": "6FA62ACC-E448-D51D-C3AA-9D4EA2BDCEA0"
}
}