In POS v10 you no longer need to receive any information from MobilePay to get started calling on behalf of a merchant.
Based on a merchant VAT-number you can retrieve all needed information of a merchant, including storeId's and details of storeId.
Retreive storeId by calling GET/v10/stores
with merchant VAT-number in header: x-mobilepay-merchant-vat-number
Retrieve storeId details by calling GET/v10/stores{storeid}
Example response:
{ "storeName": "Store 1",
"storeId": "b3f69e80-f8dc-4d81-8f46-24a8fd8fbd9f",
"storeStreet": "Example City",
"storeZipCode": "1234",
"storeCity": "Example City",
"brandName": "The Brand",
"merchantBrandId": "POSDK12345",
"merchantLocationId": "10001"
}