Being able to setup more than one trigger per scenario is useful when the same kind of data comes from different sources. Ex: Leads comming from Facebook Ads, and from another, generic, webhook.
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WORKAROUND:
  1. Create a "core" scenario that would perform the common data processing. Insert the "Webhooks > Custom webhook" module at the beginning of the scenario. Copy the webhook's URL.
  1. For each trigger you would like to employ create a separate scenario and insert the corresponding trigger in it. Connect the "HTTP > Make a request" module after the trigger.
  2. Configure each "HTTP > Make a request" module to pass the data to the "core" scenario: paste the copied URL in the URL field and map the items in the Fields field.
(see the attached screenshot and https://support.integromat.com/hc/en-us/articles/360006248533-HTTP for more information about making HTTP requests)