We're updating mandate, customer, and subscription identifiers to use Mollie's longer API identifier format. This follows the earlier update to API identifiers and brings mandates, customers, and subscriptions in line with the same standard.
What's evolving?
Legacy mandate identifiers contain 10 characters after the mdt_ prefix. Legacy customer identifiers contain 10 characters after the cst_ prefix. Legacy subscription identifiers contain 10 characters after the sub_ prefix. Newly created mandates, customers, and subscriptions will use a longer identifier, with up to 22 characters after the respective prefix. The prefixes themselves stay the same.
This change applies to newly created mandates, customers, and subscriptions, including mandates created automatically through a payment. Existing mandates, customers, and subscriptions keep their current identifiers and remain usable. You do not need to recreate them, migrate customer records, or ask customers to authorise mandates again because of this update.
What does this mean for you?
If you maintain a custom integration, review any systems that store, validate, or pass mandate, customer, or subscription identifiers — including subscription platforms, billing software, CRM/customer data stores, and other connected systems:
- Database storage: Allow at least 40 characters for the complete identifier, including its prefix, for mandate, customer, and subscription IDs.
- Custom validation: Remove checks that require exactly 10 characters after mdt_, cst_, or sub_. If you validate the format, check the expected prefix without enforcing a fixed length for the remainder.
- Handling identifiers: Store and send the complete identifier exactly as returned by Mollie. Treat it as a string; you do not need to decode or interpret it.
- Compatibility: Make sure your integration accepts both existing shorter identifiers and new longer identifiers, across mandates, customers, and subscriptions.
These storage and validation recommendations follow our existing identifier migration guidance. You can also consult the API identifier documentation.
If you use a plugin or an integration maintained by another provider, check with that provider that it supports longer mandate, customer, and subscription identifiers.
The identifier change does not alter how you use mandates, customers, or subscriptions for recurring payments. However, truncating or rejecting a longer identifier could prevent your integration from retrieving a customer, subscription, or mandate, or using it in a payment request. If you encounter an issue, check that the full identifier is preserved throughout your integration and contact Mollie Support with the relevant API error and identifier.