There is a requirement in REST API which force developers to fill Ticket Fields required for AGENTS when a ticket is being created with API.
However in case when you create a ticket on behalf of end user - you can't specify Agent or Group, since End user is not able to choose it.
I'm quite sure that a lot of other integrations which create tickets on behalf of End users suffer from this API limitation. There should be possibility to create tickets with API, as an end user, not as an agent, and not meet agent's requirements.
Right now we spend a lot of time explaining our customers why their tickets are not being created and asking them to provide default values for such fields. In some cases it is not possible for them to provide such values.
P.S. Please advice if I'm missing some workaround which can solve this issue.