> **Description:** Common questions and answers about the MobilePay Online PSP integration, covering technical issues, implementation challenges, and operational concerns.

# Frequently asked questions

## Merchants

### Is it possible to prefill the phone number

Yes, it is possible to prefill the phone number. For details, see [Prefill phone number on landing page](https://developer.vippsmobilepay.com/docs/APIs/psp-mp-api/mp-psp-api-guide.md#prefill-phone-number-on-landing-page).

### How can we update merchants?

It is not possible to update merchants.
Instead, you must offboard the merchant using the *Delete merchant* endpoint,
[`DELETE:/api/v1/merchants/`](https://developer.vippsmobilepay.com/redocusaurus/psp-mp-swagger-id.yaml)
and re-onboard them using the *Create merchant* endpoint:
[`POST:/v1/merchants`](https://developer.vippsmobilepay.com/redocusaurus/psp-mp-swagger-id.yaml).

### What happens if the user navigates back to merchant checkout from the landing page?

If the user does back-navigation in the browser to return to your checkout from the landing page
**after** having submitted their phone number, **we will cancel the payment**.
This is to prevent users from paying for the same order twice.
Often, when a user navigates back to your checkout,
it will be to change a minor detail of the order (e.g., shipping address or method).
In these cases, not cancelling the payment would cause the user to have two active payments to the same merchant in the app,
often with the same amount.
To prevent user confusion, we therefore cancel the payment on behalf of the user.
Please note that if the user does this,
you will not be able to reuse the `redirectToMobilePayUrl` as the payment is no longer active.
You must therefore initiate a new payment and get a new `redirectToMobilePayUrl`.

## Testing

### Is it possible to add our own test cards to the test users

It is not possible to add your own test cards. Instead, you can use [magic numbers](https://developer.vippsmobilepay.com/docs/APIs/psp-mp-api/mp-psp-api-getting-started.md#magic-numbers-for-emvco-tokens).

> **Full site overview:** For every page in this documentation, read [https://developer.vippsmobilepay.com/llms.txt](https://developer.vippsmobilepay.com/llms.txt).