Google Analytics: What does "?__c=1" refer to? - google-analytics

I usually notice ?__c=1 in my Google Analytics Traffic Reports/Realtime, and I don't know what it refers to. I already searched for it, but I couldn't find any information!
Here's a snapshot:

Related

What is the Google Analytics client prefix?

So we can track conversions on a hotel booking widget on our website we are asked to provide the Google Analytics client prefix. They say: Your Google Analytics client prefix - Usually, the name of your property in lower case with dashes replacing any spaces, e.g. Sydney hotels would be sydney-hotels.
Anybody know where to find the Your Google Analytics client prefix?
I have searched online but couldn't find out how to do this :/
Thank You for your help!

How does google anayltics know about Google ads?

There is something quite basic that confuses me. I use Google ads conversion tracking with Google Tag Manager, and I don't understand how my google analytics know about these ads in the first place. I mean, the conversion tags I create in Google Tag Manager don't include the Google Analytics tracking code at all.
What am I missing?
Thanks
It knows based on the url structure of the incoming links.
This link gives a good overview.
UTM Codes: How to Track Campaign URLs in Google Analytics
This tool allows you to see how the different urls are built and decomposed in GA.
campaign-url-builder
Essentially the structure is integrated and google analytics logically decomposes and presents the data in a meaningful format based on URL.

google analytic not showing real time data on specific Ip

Google Analytics not showing any result on specific IP, when check on mobile GA is showing the data. The error we are getting is "Resource is not available. Please try again later.
One or more of the services on which we depend is unavailable. Please try again later after the service has had a chance to recover."
Google have a bug in Google Analytics, which they are trying to fix:
https://www.ohow.co/google-analytics-real-time-report-not-working-fix/

Google Analytics.js > track data in a website reachable by multiple domains

I can't find this answer in the official documentation.
I'm tracking google analytics data on mycustomerwebsite.com
But the website is also working and reachable in seofriendlydomain.com
Website is the same, so I include analytics.js data in both of them.
My customer asks, to know how much traffic comes from each domain,
not needing complete data but only few stuff like % of incoming visitors or number.
I found similar topics:
Google Analytics multiple domains one website
Why there is no answer ? is there no solution ?

How do you setup a Google Analytics account for a website that already has the tracking code?

I have FTP access and am re-designing a website and I want to see historical traffic data from their Google Analytics, but they do not have a Google Analytics Account and can not get in touch with their last web person who set it up.
The tracking code has been in place for several years. There are a lot of articles about how to add Google Analytics code to a website but how do you setup a Google Analytics account with tracking code that is already there?
The best way is to ask person who set it up. But if it is impossible - here is the article, which help You - http://savvydealer.com/reclaim-your-google-analytics-account/
This is the only one way.
There are 2 options,
Ask for the Authoritative person to add you as an Admin, so you can easily get access. If this option may not possible then,
You can replace old tracking code with new tracking code.

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