create-update-lead-form.html

%%[
IF RequestParameter("submitted") == true THEN

/* check if lead already exists */

  SET @subscriberRows = RetrieveSalesforceObjects(
   "Lead",
   "Id,Email",
   "Email", "=", RequestParameter("email")
   )
  
  /* get lead id if lead exists */
  
  IF RowCount(@subscriberRows) > 0 THEN 
  SET @leadId = Field(Row(@subscriberRows, 1), "Id")
  
  /* update existing lead */
  SET @updateRecord = UpdateSingleSalesforceObject(
      "Lead", @leadId,
      "FirstName", RequestParameter("firstname"),
      "LastName", RequestParameter("lastname"),
      "Company", RequestParameter("company")
     )

  ELSE
   /* create a new lead */
  SET @leadId = CreateSalesforceObject(
        "Lead", 4,
        "FirstName", RequestParameter("firstname"),
        "LastName", RequestParameter("lastname"),
        "Company", RequestParameter("company"),
        "Email", RequestParameter("email")
       )
  ENDIF       
]%% 
<h2>Thank you for submitting the form.</h2>

%%[ ELSE ]%%

<table style="padding: 20px;"><tr><td>
      <h2>Please fill in the form:</h2>
      <form action="%%=RequestParameter('PAGEURL')=%%" method="post">
         <label>First name: </label><input type="text" name="firstname" required=""><br>
         <label>Last name: </label><input type="text" name="lastname" required=""><br>
         <label>Company: </label><input type="text" name="company" required=""><br>
         <label>Email: </label><input type="text" name="email" required=""><br>
         <input name="submitted" type="hidden" value="true"><br>
         <input type="submit" value="Submit">
      </form>  
</td></tr></table>

%%[ ENDIF ]%%