Specify preferences for a payment plan for a web enrolment. 

If the enrolee wishes to pay for an online enrolment in instalments, call this function to specify the enrolee's preferences for their payment plan for this enrolment. This includes the instalment frequency, and the amount to pay per instalment. 

Note that this function only pre-populates the payment plan in VETtrak for the invoice generated when this web enrolment is manually processed. It still requires the VETtrak user to complete the setup for the payment plan in VETtrak after processing the web enrolment - the VETtrak user can modify the payment plan or cancel it if required. 

Also note that if you automatically process the web enrolment through the API, a VETtrak user will not get an opportunity to process the payment plan. In this case, your system should inform a user that the student wishes to pay with a payment plan, with instalment amount X, frequency Y, for invoice number Z, so the user can do so in VETtrak. 

Calling this will cause an invoice to be generated, even if AddWebInvoice is not called. You can optionally call AddWebInvoice if you wish to specify more details for the generated invoice. You can optionally call AddWebPayment if you also wish to record details of a deposit payment that was collected up-front, in which case the total amount to be collected by the payment plan will be the outstanding amount on the invoice after that payment is applied. 

Requires a valid registration key entry for the Payment Plan add-on feature. 

This function has security level "Protected", and can only be accessed by users that have explicitly been granted permission to the API.

[WebMethod(Description = "Records the specified payment plan data against the existing web enrolment ID")]
public TAuthenticate AddWebPaymentPlan(string token, int webEnrolId, int frequency, decimal instalmentAmount);