I am registering a batch of 500 transactions in a java application with web3j and after a while it gives me this error:

java.lang.RuntimeException: Error processing transaction request: replacement transaction underpriced Output from Server

And the application code, register transaction in the smartcontract.

public String CrearCertificado(CareerCertificate careercertificate, String id, String fecha, String nombre, String rutalumno, String instituto, String rutinstituto, String titulo,
String totalhash, String fechatitulacion, String registronumber, String codigoV) throws Exception {

String txhash;
txhash = careercertificate
        .createCertificate(id, fecha, nombre, rutalumno, instituto, rutinstituto, titulo, totalhash, fechatitulacion, registronumber, codigoV)
if(txhash !=null || !txhash.equals("")){
        return txhash;
}catch(Exception e){

    System.err.println("Error 222-2 interno en el Metodo CrearCertificado en la clase  Conexion.java: "+e);

    id = null;
    fecha= null; 
    nombre= null; 
    rutalumno= null; 
    instituto= null; 
    rutinstituto= null; 
    titulo= null; 
    totalhash= null; 
    fechatitulacion= null; 
    registronumber= null; 
    codigoV = null;
return "222-1";


To load the Contract

private CareerCertificate loadContract(String contractAddress, Web3j web3j, Credentials credentials) {

return CareerCertificate.load(contractAddress, web3j, credentials, GAS_PRICE, GAS_LIMIT);


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