The main issue was in MailJetClient.cs line 450 where MetaSenderData was copy/pasted as the type for GetContactData(). I fixed that to be the correct type for ContactData protocol.
https://dev.mailjet.com/email-api/v3/contactdata/
However, I noticed a significant naming inconsistency with the data objects. In the MailJet API, "ContactData" is actually what you had called ContactDataUpdate. And what you previously called ContactData is actually a the object needed for the response for ManageContact (add to list):
https://dev.mailjet.com/email-api/v3/contactslist-managecontact/
So I renamed this to "ContactResponse". Not sure what the best thing to call it is. I can't stand some of MailJets naming of things, but I guess it might be better to keep things named as closely to their API as possible so that one easily understand/compare the MailJet API to this C# library.
The main issue was in MailJetClient.cs line 450 where MetaSenderData was copy/pasted as the type for GetContactData(). I fixed that to be the correct type for ContactData protocol. https://dev.mailjet.com/email-api/v3/contactdata/
However, I noticed a significant naming inconsistency with the data objects. In the MailJet API, "ContactData" is actually what you had called ContactDataUpdate. And what you previously called ContactData is actually a the object needed for the response for ManageContact (add to list): https://dev.mailjet.com/email-api/v3/contactslist-managecontact/
So I renamed this to "ContactResponse". Not sure what the best thing to call it is. I can't stand some of MailJets naming of things, but I guess it might be better to keep things named as closely to their API as possible so that one easily understand/compare the MailJet API to this C# library.