Only logged in users can change billing and recurring amount
Two bits are required for anonymous users to be able to access URLs like:

/civicrm/contribute/updatebilling?reset=1&amp;coid=4263&amp;cs=b88004e51f6c99b0601aceab7e489315_1530392348_168


Permissions: make online Contributions
Administer -> CiviContribute -> IATS Payments Settings
Check the box: Enable self-service to recurring contribution Contact Billing info:




PS - as you may have noticed this is no longer working in higher 5.x versions of CiviCRM. This regression can be fixed with this solution (PR) which was posted here: https://github.com/civicrm/civicrm-core/pull/12668 - unfortunately it was closed. It's only one line of code you need to add to this file: CRM/Contribute/Form/UpdateBilling.php



$processorParams['recur_id'] = $this-&gt;_subscriptionDetails-&gt;recur_id;