What is "Form Action" field in HTTP form-based authentication to deliver OTP..??

Dear Team,

We have an access policy configured on our bigip APM device with 2-factor authentication (integrated with nexus hag). now we are planning to remove nexus hag from the access policy and let APM device itself deliver the OTP to user's for authentication.

We are referring below document to achieve this,

https://techdocs.f5.com/en-us/bigip-15-1-0/big-ip-access-policy-manager-authentication-methods/one-time-password-authentication.html#GUID-7EFD0E56-5059-44B2-8978-AB4373A5CF22

In "Configuring HTTP form-based authentication to deliver a one-time password" section.

No.6. In the Form Action field, type the complete destination URL to process the form.Specify a URL for a form action that you created to send a user a one-time password using an SMS.

in the above line which destination URL, they are talking about. Is it the URL for SMS gateway..??

Also which credentials we have to provide in Username and password section. is it mandatory..??

can anyone help me on this..??

Regards,

Venkatesh Mudiraj