My application needs to send a payment link to the customer via SMS. Capture the payment and the send a payment received notification back to the customer via SMS. I have gone through the Zoho books API and I observed:

1) No API to generate payment link

2) From my zoho books account, I manually generated a payment link and tried sending it both to my number as email. I received by the email but not sms. I have integrated a twilio account. 

3) The access token is valid only some 3600 secs. But in a real time project generating it every time is not feasible. 

Can I get some help on this?