With the acquisition, Paytrail and Checkout Finland have merged into the same company and payment services will be merged. You can read more about this in the Paytrail news here: https://www.paytrail.com/en/news/paytrail-and-checkout-payment-services-will-be-merged-on-05.10.2021
The new Paytrail will work with Checkout’s current management and interface. In practice, this means that the current Checkout service will have a new Paytrail look in its own admin pages as well as in the online store payment method.
For e-commerce, merchants using the old Paytrail will receive new IDs from Paytrail for the e-commerce payment method. After that, you need to add a new payment method in the store, copy the IDs to it and display the new payment method in the store. After testing, you can then hide the old one.
More detailed step-by-step instructions will be available as soon as Paytrail and the e-commerce payment integration have undergone the brand changes.