Upon starting the payments which properties are required?
Are TraceId required for earlier initialized token payments after 2021.02.01?
First yes, TraceIds are not required for earlier initialized token payments without 3DS for an INTERIM period. After this period expires (potentially 2021 Q3) TraceIds will be required for all Token Payments.
We've received TraceId in the following format:
The TraceId is generated by the card issuer, and can be anything up to 100 characters. Whitespaces and 0s should also be left intact.
Can we skip the additional data in subsequent payments that were required for 3DS authentication in the first Token Payment?
Wrong! The difference between the initial and subsequent token payment is that 3DS authentication is only required for the first, initial payment. More info can be found here
Do we have to generate the TraceId in the first Payment/Start, or is it generated by Barion?
TraceId is generated by the Card Issuer, so it is not required in the initial Payment/Start request. You have to store the TraceId, received in the GetPaymentState response, and send it in all subsequent payments. You can read more here. The exceptions are the subsequent payments of an already initialized token payments without 3DS. More info can be found here
When the amount of the first payment is different than the rest, I have to use MechantInitiatedPayment and not Recurring. Right?
Yes, RecurringPayment can only be used, when the amounts of all the subsequent payments are the same. If only 1 is different (eg. you give discount/free for the first month), only MechantInitiatedPayment can be used. You can find more info here.