To connect Facebook and Instagram ads, open your Property and choose Connect Meta. Meta asks you to approve access, then Ads Arsenal shows the ad accounts your Meta login can see. Tick the ones that belong to this Property and choose Link selected accounts. Data starts flowing within minutes of connecting for most accounts, up to an hour for large ones.
Connect with the Facebook login that can open the ad account in Meta, either directly or through your Business Manager. You do not need to be a Business Manager admin; you need access to the ad account itself.
Meta shows these on its own screen every time you connect, so you always see exactly what you are granting.
The Facebook login you used cannot open any ad account. Check in Meta that this login has access to the ad account (in Business Manager, under the ad account's people), or ask someone who does to connect instead. Then choose Try connecting again.
The picker lists the Facebook Pages your login shared with Ads Arsenal. If a Page is missing, choose Share more Pages and tick it in Meta's dialog. Tick every Page you want, not just the missing one: Meta's dialog replaces your previous choice each time. If an ad runs from a Page outside the list, Ads Arsenal tells you so.
To add another ad account later, choose Connect Meta again from the Property's Settings, under Accounts. Accounts already linked stay linked. If access expires or is removed, reconnecting the same account picks up where it left off: its history is kept.
Email bishop@battlebridge.com with the step you are on and the exact words of any error (a screenshot is perfect). A person reads it.