By default Symplify will send to all Measuring IDs found on your website. If you want to limit this you need to enter the Measurement ID for the one(s) you want to send to.
This is done in website settings. You can see this setting by clicking My websites -> click website -> Edit website -> Tracking -> Limit the Google Analytics Sync.
Here you enter the Tracking ID/Measurement ID for the ones you want us to sync with (whitelist). Multiple ID's are entered comma separated. Example: G-XXXXXXX, G-XXXXXXX, etc.
NOTICE: If you are using GTM to implement GA4 you will need to set up an trigger/tag per Measuring ID. Read more about this in the Send only to specified Measurement ID(s) section here.
Get the correct ID
Measurement ID should not be mixed with Property ID. To find your Measurement ID in GA4 navigate to Admin -> Data Streams -> (Your websites Data Stream).