Failed to get transactionId in links/link/init

transaction id is required in the body of this API request, where would i get this transaction Id from? or do i have to call some other API before it to get the transaction Id? currently on giving a random transaction Id, i am getting the following error :-
{

"error": {

    "code": 1427,

    "message": "Failed to get transaction Id"

}

}

@IntegrationSupport