write code for check box in Adobe Form

Here is a basic code in javascript to this..
First add an eventlistener to the checkbox element.

document.getElementById("sameAsBillTo").addEventListener("click", copyInfo);

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And the function

function copyInfo() {
    // Get the checkbox element
    let checkbox = document.getElementById("sameAsBillTo");

    // Get the "Bill To" and "Ship To" fields
    let billToCompany = document.getElementById("billToCompany");
    let billToAddress = document.getElementById("billToAddress");
    
    let shipToCompany = document.getElementById("shipToCompany");
    let shipToAddress = document.getElementById("shipToAddress");
    
    // Check if the checkbox is checked
    if (checkbox.checked) {
        // Copy the information from the "Bill To" fields to the "Ship To" fields
        shipToCompany.value = billToCompany.value;
        shipToAddress.value = billToAddress.value;
     
    }
}

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I have some issue make your code work.
I created below and working pretty well, except:
Last two lines, entry for phone#  not working. Is any limitation in that kind of code how many lines I can use it ?
if I eliminate let say Country phone fields are working.

if (event.target.value=="Yes") {
      this.getField("CompanyST").value = this.getField("Company").value;
      this.getField("CompanyST").readonly = true;
     this.getField("AddressST").value = this.getField("Address").value;
      this.getField("AddressST").readonly = true;
     this.getField("CityST").value = this.getField("City").value;
      this.getField("CityST").readonly = true;
     this.getField("StateST").value = this.getField("StateProvince").value;
      this.getField("StateST").readonly = true;
     this.getField("AddressST").value = this.getField("Address").value;
      this.getField("AddressST").readonly = true;
     this.getField("ZIPST").value = this.getField("ZIP").value;
      this.getField("ZIPST").readonly = true;
     this.getField("CountryST").value = this.getField("Country").value;
      this.getField("countryST").readonly = true;
     this.getField("Phst").value = this.getField("Phone").value;
      this.getField("Phst").readonly = true;


}

Check your console for errors message and post it