groovy markup java.lang.Exception: No method named issue

Good day.

I am working on this groovy script

import groovy.xml.MarkupBuilder;
import groovy.xml.*;

def writer = new StringWriter();
def xmlResponse = new MarkupBuilder(writer);
def index = 0;

xmlResponse.CalculatePayoutFigureResponse() {
    Identifier([UniqueID:'CalculatedLoanRepayment-1'])
}
String response =  writer.toString();
return XmlUtil.serialize(response);

Every time this gets called, I am getting the ff error:

    SEVERE: java.lang.Exception: No method named 'Identifier' found for arguments [[UniqueID:CalculatedLoanRepayment-1]]
java.lang.Exception: No method named 'Identifier' found for arguments [[UniqueID:CalculatedLoanRepayment-1]]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
        at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:80)
        at org.codehaus.groovy.reflection.CachedConstructor.doConstructorInvoke(CachedConstructor.java:74)
        at org.codehaus.groovy.runtime.callsite.ConstructorSite$ConstructorSiteNoUnwrap.callConstructor(ConstructorSite.java:84)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:247)

Anyone familiar with this? Can you point me to the correct direction.

I have been looking for solutions but to no avail. Is the way I am building the XML wrong? I am using groovy 2.4.4.

THanks in advance!
Chris

After doing some tweaks to the code, I was able to make this work. I used the MarkupBuilder object before every element I am trying to add. Code became like this:

xmlResponse.CalculatePayoutFigureResponse() {
    xmlResponse.Identifier(UniqueID:'CalculatedLoanRepayment-1')
}

I got the output that I expected.

<CalculatePayoutFigureResponse>
   <Identifier UniqueID='CalculatedLoanRepayment-1' />
</CalculatePayoutFigureResponse>

No idea though as to why this solution worked and what caused the issue I initially encountered.

Thanks! -Chris