Your software
My Mautic version is: v2.16.2
My PHP version is: 7.3.17
Your problem
My problem is:
I would like to add the Referrer URL that is already under “Toggle Details”, to the Contact Details.
Therefore i created a Custom Field and named it Referal.
The hidden field that saves the Referrer URL locks like this: (Screenshot)
We would like to filter users according to there Referrer URL
This should do the trick 
Best,
Ekke
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Thanks for this, i tried but somehow it does not save it to the Custom Field.
What i am missing are the Rights of the Custom Field. Thats how i did it:
Then the hidden Form, that is mapped to the Custom Field, also there i do miss some settings.
Do i need to click “Save result” or not? And how about behavior, do i need to click “Show when value exists” No/Yes and “Auto fill data” No/Yes
Probably thats the reason why it does not save it.
Let’s start with the custom field:
What i am missing are the Rights of the Custom Field.
Can you explain what you mean by that? What is the symptom?
it works now.
It saves the “Referal” to the Custom Field “Referal”. So far happy.
Now i am working on Segment those contact with a specific Referal URL. But i do not get any result by doing this. Also not, if i include the exact same URL that is in the contact Field - Referal Saved.
Yeah, glad to hear that!
For the segment filter: Can you give a specific example? There are so many ways to go (contains, regexp, …)
I tried many of them. Name, Referal, for example. (referal ist the custom field i created according the how-to from you)
Anyway, i tried “equal”, “contains”, „not empty“, „ends with“ „like“ etc, but none of them showed a contact. Always “no contact”.
Do i miss something? Probably yes 
If i open Tab Contacts, i can see i do have there 14 Contacts, but with segments, filters, i definitely can not filter them
