Question from Reddit:
I have a PageView event that I upload via Conversions API. As part of the event’s parameters, I supply event_source_url.
I have three custom conversions right now. With condition that URL contains “/somepage-1”, “/somepage-2”, “/somepage-3” respectively.
Can I create a new custom conversion with a condition that URL matches “/somepage-” and expect it to match the same evens as all my three other custom conversions? Without interrupting my original three custom conversions?
I assume yes, but support told me no. Which doesn’t make sense to me.
If the answer is yes, can I create an ad set that optimizes for this combined custom conversion without any detrimental effect for other existing ad sets that optimize for each of my three original custom conversions separately?
Again, I assume yes. But just want to confirm.
Finally, that fourth ad set that would optimize for my combined conversion, would it be at any disadvantage or would it be as if it were any other custom conversion and the system would optimize to target users who are likely to convert for what’s essentially any of my three original conversions?
That’s what I’m trying to achieve, but again, support wasn’t of much help, so I’m asking here.
Thanks.
Answer from Nabil:
The short answer is:
Yes, you absolutely can create a new custom conversion with a broader URL condition, like URL contains "/somepage-", and it will correctly match all events that currently match your three narrower custom conversions, without interrupting them.
Your support contact was likely incorrect.
This new, combined custom conversion can be used for optimization in a new ad set, and it will function as a single, valid optimization signal.
This new ad set will be at an advantage because you are immediately providing it with a larger, more comprehensive data set (more conversion volume) to learn from, allowing the ad delivery system to optimize more efficiently for users likely to complete any of your three original conversion actions.
The long answer is:
Your understanding of how Facebook’s custom conversions work is correct, and the support response you received is puzzling.
Custom conversions are essentially filters applied retroactively to your incoming event data, and they are entirely non-exclusive.
Think of it this way: your PageView event comes in via the Conversions API with the event_source_url parameter set to, for instance, https://example.com/somepage-1/confirmation.
Your original three custom conversions—let’s call them CC1, CC2, and CC3 – each look at that single event and check their respective conditions.
If the URL contains /somepage-1, CC1 scores a hit.
If you then create a new custom conversion, CC4, with the condition URL contains "/somepage-", CC4 will also look at that same event and score a hit, as the URL clearly contains the common fragment.
Custom conversions operate independently, and creating a broader one does not negate the narrower ones.
Since all four custom conversions are now scoring hits on the same underlying PageView events, they can all be used simultaneously for different optimization goals.
This leads directly to your second question about ad set optimization.
When you create a fourth ad set that optimizes for your combined custom conversion (CC4), you are giving the Facebook algorithm a much larger volume of data points to optimize against, as CC4 now encompasses the volume of CC1, CC2, and CC3 combined.
This is a crucial advantage for optimization because the Facebook system, particularly during the learning phase, performs better with more frequent conversion data.
It will indeed optimize to target users who are likely to convert for the combined action – that is, anyone who is likely to land on any page starting with /somepage-.
This strategy is, in fact, an excellent best practice for consolidating small-volume conversion events into one larger signal for more efficient ad delivery.
A robust way to manage this entire setup and ensure the highest data quality is to utilize Facebook Conversions API combined with a server-side tagging solution like Stape or Google Cloud Platform and orchestrate the data flow via Google Tag Manager.
This server-side architecture ensures your PageView event and its crucial event_source_url parameter are sent directly to Facebook’s servers, bypassing browser-side issues like ad blockers and increasing the overall match rate and reliability of your custom conversions.
You would use client-side GTM to collect the URL and send it to your server container, which then forwards the data to the Facebook Conversions API.
This solid foundation ensures that when you create or edit custom conversion filters in the Ads Manager, they are working with the most complete and accurate data set possible.
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