Explanation
You are only able to build similar audiences based on the following seed audiences:
1. Facebook Fan Page
2. Custom Audiences: email databases, customer databases, interactions with the fan page, website visitors with pixel and interactions with lead ads.
Keep in mind that you are NOT able to build similar audiences using core/saved audiences on Facebook.
Similar audiences need to be built from users who have interacted in some way with one of your digital assets (Fan Page, Mobile App, Website, CRM and so on); whereas, core/saved audiences are used to find users based on demographics, interests, behaviors, and other variables who have NOT interacted with one of your digital assets.

Explanation
Here is a full list of all the different measurement solutions you can currently run through one of Facebook partners.
It's key to understand how each solution fits for different cases.
Audience Outcomes - Facebook Partners
* Nielsen DAR: Measures campaign reach across Facebook, Instagram, and other publishers.
* Nielsen TAR: Measures campaign reach across Instagram, Facebook, and television.
* Viewability Verification Partners: Verifies viewability metrics for Facebook and Instagram through
* best-in-class viewability partners.
Brand Outcomes - Facebook Partners
* Nielsen Brand Lift: A Nielsen product created to measure the impact of Facebook media on brand perceptions.
* Millward Brown Brand Lift: A Millward Brown Digital product that is designed to help marketers quantify the results of their advertising on Facebook and Instagram.
Sales Outcomes - Facebook Partners
* Partner Lift: Facebook's Partner Lift integrations leverage best-in-class vendors to measure lift in sales using partner-based ROI measurement solutions.
* MTA Partner Program: Facebook offers an MTA Partner Program that enables multi-touch attribution (MTA) partners to provide people-based MTA reporting across all publishers, including Facebook.
* Marketing Mix Modeling (MMM) Partners: Enable partners to better measure and compare the effectiveness of advertisers' marketing channels in terms of contribution to sales, efficiency, and ROI.
* Mobile Measurement Partners (MMPs): Work with one of our Mobile Measurement Partners to see aggregated reporting across multiple ad networks, powered by Facebook attribution data.

Explanation
You receive a month-long IO from a client for a new campaign with a $10,000 budget.
To manage this:
* Create a new campaign (or duplicate an existing one).
* Set a campaign spending limit of $10,000.
* Ensure the start and end dates for the ad sets in the campaign align with dates of the new IO.
* Make sure the sum of the budgets for the active ad sets in this campaign reflect that you want $10,000 to be spent over the course of the month. The campaign spending limit is an un-paced limit, so for smooth pacing, make sure the sum of the budgets for active ad sets in this campaign reflect that you want
$10,000 to be spent over the course of the month.
The IO is increased to $15,000.
To manage this:
* Edit the campaign spending limit for the existing campaign to $15,000.
* Ensure the sum of the budgets for the active ad sets in the campaign reflect that you want to spend
$15,000 over the course of the month, starting from the original start date of these ad sets.
The IO is decreased to $9,000.
To manage this:
* Edit the campaign spending limit for the existing campaign to $9,000.
Note: This can only be done if the amount spent on the campaign so far is at least $100 less than the new limit.
In this scenario, that would mean no more than $8,900 could be spent so far in order to lower the limit to
$9,000.
* Ensure the sum of the budgets for active ad sets in this campaign reflect that you want $9,000 to be spent over the course of the month, starting from the original start date of these ad sets.
The IO is delivered in full by the end of the month. You receive a new IO for the next month with a budget of
$20,000.
You have two options for setting a new campaign spending limit here:
* Option 1: Start a new campaign
* Create a new campaign (or duplicate existing one).
* Set the campaign spending limit for the new campaign to $20,000.
* Ensure end date for the ad sets in new campaign align with end date of the new IO.
* Option 2: Continue working on an existing campaign
* Raise the campaign spending limit on the existing campaign to $30,000.
Crucial: The campaign spending limit on an existing campaign will always reflect prior spend, even if the limit is removed and then reapplied. In this case, the campaign has already spent $10,000. In order to allow for an additional $20,000 of spend, the campaign spending limit must be set to $30,000 (previous spend of $10,000 + new IO amount of $20,000).