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Since 2021-12-07, participants are recommended to cache the Participant Metadata Set for up to 1 hour before making an attempt to update it. This value is specified by the Cache-Control max-age response header. After that it is recommended to use ETag and the If-None-Match request header to conditionally get a new Participant Metadata Set only if it is updated. If update is not possible for some reason, the previously fetched Participant Metadata Set is valid for 7 days.

Reference

More information in MTS4, found at https://bitbucket.org/samtrafiken/bob-mts-4-coordination-and-key-management/src/master/mts4.pdf