Hi @Mustafa Altuntaslar ,
Welcome to Microsoft Q&A forum and thanks for reaching out. By reading this statement - "We use MS Dynamics 365 and our Marketo instance is linked to our CRM" - my understanding is that your Marketo instance is integrated with CRM.
Unfortunately Marketo instances that are integrated with external CRM are unsupported. The product team is considering it to be the feature request to support external CRM in Marketo connector.
This is the reason unable to load the tables/entities even though you are able to establish the connection.
Ref: Here is a MSDN thread with similar discussion: https://social.msdn.microsoft.com/Forums/en-US/48375c22-d6a6-4c54-b05d-0f6667566db1/marketo-connector-throws-error-opportunity-api-disabled-unknown-error-code?forum=AzureDataFactory
Hence, I would recommend you to please log a feature request in ADF user voice forum - https://feedback.azure.com/forums/270578-data-factory
All the feedback shared in this forum are actively monitored and reviewed by ADF product team. Also please do share the feedback link here once it is posted so that other users with similar idea can upvote and comment on your suggestion which would help to increase the priority of feature request.
Hope this info helps.
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