Update transition-to-one-platform.md

Author: HenrietteBossen

docs/online/transition-to-one-platform.md

@@ -59,5 +59,8 @@ If you have hardcoded dependencies make sure you allow for these.
 Example:
  "redirectToMobilePayAppUrl": "vipps://?token=(TOKEN)"
 
+## Prefill phone number
+It is currently not possible to prefill the phone number on the MobilePay landing page. If a phone number is supplied the page will simply ignore it. Instead users can use the "Remember me" functionality to avoid having to input phone number each time. We are looking into adding the prefill option again but have no ETA for this yet. 
+
 ## Test availability
 The sandbox environment will not be migrated to the new platform and therefore it will not be possible to test the Online facade. We are working on a test solution but currently there is no estimated time for its availability. As an alternative you can test in production but perhaps limit the capture option in order to ensure funds are not being transferred.