At various points in the Opportunity specification the use of ISO 8601 data/time formats is required. However, despite very widespread implementation, ISO 8601 is not an open standard and is in fact paywalled by the ISO.
Consider shifting to RFC 3339 instead. A nice summary of the differences between RFC 3339 and ISO 8601, and in particular the more restricted scope of RFC 3339, can be found here. The question of whether these restrictions affect plausible OpenActive use-cases will need to be considered.
At various points in the Opportunity specification the use of ISO 8601 data/time formats is required. However, despite very widespread implementation, ISO 8601 is not an open standard and is in fact paywalled by the ISO.
Consider shifting to RFC 3339 instead. A nice summary of the differences between RFC 3339 and ISO 8601, and in particular the more restricted scope of RFC 3339, can be found here. The question of whether these restrictions affect plausible OpenActive use-cases will need to be considered.