Enabling ‘Soft Cap Budgets’ will help the line cap at a specified budget, but is not a guarantee.  It is possible that a Line Item configured with a ‘Soft Cap’ budget will spend more than the allocated budget. This happens because the bidders are placing simultaneous bids on ad slots in order to win impressions, while updates for spend are slightly delayed. This allows the bidders to continue bidding although the soft cap budget may have already been met. By the time the spend for the Line Item is updated, it is possible the Line has already spent more than the allocated budget. This is most typical with Lines that have small budgets and/or open targeting. 
If this is happening for one of your Line Items, there are several steps that you can take to try to combat this overspend and limit delivery. These steps are not guaranteed to restrict the Line to the exact Soft Cap Budget amount, however, they should help to limit spend as well as improve campaign performance. 

1. Remove Exchanges with Low Performance
   Enter into the Reporting tab and select the Advertiser and Line you wish to evaluate and update the report. Scroll down to the ‘Exchanges’ section. In this section you can evaluate each Publisher through which your ad has been served and the corresponding CTR. Campaign performance can be increased and spend restricted by removing Exchanges with low performance. To remove an exchange open the Line Item Targeting settings and in the ‘Exchanges’ tab select the red ‘minus’ sign next to the Exchange name. The Exchange should move from the right side of the window to the left and appear with a green plus sign next to the name. This indicates that you are no longer buying through this exchange. For information on Pontiac Exchange reporting see here: Exchange Reporting. 
2. Add Geographic Targeting/Restrictions
   Geographic targeting is available by Country, Region, DMA, Zip Code or Latitude and Longitude. Restricting the geographic areas where the campaign will serve will limit the number of available impressions and thereby help to limit delivery. By selecting regions or areas most relevant to campaign, this will also help to ensure that you are reaching your target Audience. See more information on Zip Code or Lat/Long Audiences here: Zip Code Audience, Lat Long Audience
   If you would like to keep the geographic targeting relatively open, we recommend visiting the Reporting tab and evaluating the performance of each region or country then removing the lowest performing areas. This will also help to boost campaign performance for your selected KPI. See additional information on Geo Reporting on the following pages: Geo Region Reporting, Geo Country Reporting
3. Add Audience Targeting
   Targeting a specific Audience will limit the available users that can be served your ad and therefore restrict delivery. By targeting across behavioral, contextual or demographic variables you can also limit your viewers to those most likely to be interested in your good or service. Pontiac offers a wide variety of Audience solutions including Remarketing segments, Third-Party Audiences and Onboarded Audience integrations including onboarded CRM data, custom contextual segments and geo-framed Audience segments. See all of our Audience solutions here: Audiences.
4. Add a Site ‘Allow List’ from Top Performing Sites
   Enter into the Reporting tab and select the Advertiser and Line you wish to evaluate and update the report. Scroll down to the ‘Site Domain’ section. In this section you can evaluate each Site that the ad has been published on and the corresponding CTR. By selecting the highest performing sites and creating a site list, you can serve only on these sites and effectively limit spend as well as improve performance. You could also create a custom site list of websites with contextually relevant content to the campaign or those most likely to be visited by your target Audience. In the ‘Inventory’ tab we also have created several pre-built site lists with high performing domains that are named by content category. For more information on Site Domain Reporting and creating custom Site lists see the following pages: Site Domain Reporting, Site List Targeting.
5. Add a Viewability Threshold
   In the Line Item Targeting settings there is a feature to enable a Viewability Threshold. If this feature is enabled the platform will determine how likely an impression is to be viewable through pre-bidding technology, and will only bid on ad slots deemed above the threshold. Per IAB guidelines, an ad is considered viewable if 50% of the pixels are in-view for 1 second or more. This will limit available impressions restricting the spend of the Line Item and it could also greatly improve performance as your ads are more likely to be viewed by the user. For more information on the Viewability Threshold see here: Viewability Threshold
6. Remove Creatives with Low Performance
   In the Reporting tab, metrics are readily available by Creative. This information can be used for manual optimization, to remove low performing Creatives and to direct more of the budget towards high performing ones. For example, if a Creative has received 70% of the budget, but only 5% of the clicks, this Creative should be removed from the campaign. See more information about Pontiac Creative reporting here: Creatives Reporting.