[SalesForce] Insert Parent and multiple child record with same vf page

My query is when I input account details after that input contact detail and click on the save button its not save given error is

Insert failed. First exception on row 0; first error: FIELD_FILTER_VALIDATION_EXCEPTION, Value does not exist or does not match filter criteria.: [AccountId]*

controller:-

public class AccountContactController{
public Account acc{get;set;}
public List<Contact> cont{get;set;}
public AccountContactController(){
    acc = new Account();
    cont = new List<Contact>();
    AddRow();
    AddRow();
    AddRow();

}
public void AddRow(){
    cont.add(new Contact());

}
public void save(){
    if(acc.name != null){
        insert acc;
        List<contact> con = new List<contact>();
        for(Contact c : cont){
            c.AccountId = acc.id;
            con.add(c);

        }
        if(con != null){
            insert con;
        }
    }

}}

—-vfpage—–

  <apex:page controller="AccountContactController">
  <apex:form >
      <apex:pageBlock >
        <apex:pageblocksection columns="2">
        <apex:inputField value="{!acc.name}"/>
        <apex:inputField value="{!acc.phone}"/>
        <apex:inputField value="{!acc.website}"/>
        <apex:inputField value="{!acc.Sic}"/>

    </apex:pageblocksection>      
    <apex:pageBlockSection columns="1">
        <apex:pageBlockTable value="{!cont}" var="contacts">
            <apex:column headerValue="First Name">
                <apex:inputField value="{!contacts.firstname}"/>
            </apex:column>
            <apex:column headerValue="Last Name">
                <apex:inputField value="{!contacts.lastname}"/>
            </apex:column>
            <apex:column headerValue="Email">
                <apex:inputField value="{!contacts.email}"/>
            </apex:column>
        </apex:pageBlockTable>
    </apex:pageBlockSection>
   <apex:pageBlockButtons >
    <apex:commandButton value="Save" action="{!save}"/>
    <apex:commandButton value="Add Row" action="{!AddRow}" immediate="true"/>
    </apex:pageBlockButtons>

  </apex:pageBlock>