Cannot connect a new source
To connect to The Trade Desk you need MyReports API access (including Scheduling API access and permission to create reports). Contact your Trade Desk Account Manager for more details.
If you have double-checked your credentials with The Trade Desk, the next step is to make sure that you have connected the right report level. There are two options available: Advertiser report level or Partner report level.
I can't see my Advertiser ID when connecting The Trade Desk to Funnel
When connecting on Advertiser report level Funnel will fetch the first 1500 Advertisers connected to that Partner ID. If you have more than 1500 Advertisers connected to your Partner ID that might be the reason you can not see it.