Existing Merchant IDs haven’t changed. Beginning on March 13, 2023 new Merchant IDs created could be in the 64-bit signed range. Through a slow rollout over the next few months, a higher percentage of new Merchant IDs will be in the 64-bit signed range. By June 2023, all new Merchant IDs created will be in the 64-bit signed range.
To avoid any issues, please make sure your applications are fully compliant with IDs within a range of 64-bit signed integer values.
If you have any questions or concerns, please don't hesitate to contact us via the forum.