One Facebook ad account per campaign today. If your spend is split across accounts, the workaround is to upload the combined conversion counts to a sales lift study instead.
What the limit is
It is a product limit rather than a methodological one. Halo effect reads one connected Facebook ad account per campaign, so an advertiser running several accounts, or an agency running a client across accounts, cannot connect all of them.
The workaround is to export conversion counts from the accounts you cannot connect and upload them to a sales lift study. You lose the channel-level granularity and keep the incrementality read.
Which channels are supported
Google Ads, Google Analytics, and Facebook are supported. There is no TikTok integration and no Taboola integration. Both have been requested by customers and neither exists today.
Where no connector exists, the same causal analysis can sometimes be run on an exported file, which is how a large retail advertiser has been handled. Ask rather than assuming the answer is no.
Why halo results can come back empty
Connections sometimes appear to save and then do not persist once the account IDs are entered, occasionally with a Facebook error behind it. The visible symptom is empty halo results, which reads like the campaign had no effect.
If halo comes back empty, check that the account connection is still in place before drawing a conclusion. This is a known issue, so tell us rather than re-planning around the result.
Authorization needs view or read access on the account. You are not granting anyone the ability to change your campaigns, which is usually the question behind the hesitation.
Common misconceptions
Myth: Empty halo results mean OOH did nothing.
Reality: Check whether the account connection persisted. Connection failures present as empty results.