When using the DotDigital connector, if you receive an onscreen message informing you that you have reach their API usage limit.
This means that Dot Digital's API thinks that too many records has been called to/from your account. DotDigital have two types of Rate Limiting types: Tiered or Flat. We recommend that you head to DotDigital and change your Rate Limiting type to 'FLAT'
https://marketing.developer.dotdigital.com/docs/call-rate-limits