Hi Abdul,
The extension user is in a Site configuration.
When you start an external number, the NumberPlan is consulting... You need to match the number with the number plan.
Read the documentation below and the information "Number Plans" You have the response on how to configure and resolve your problem.
https://help.mypurecloud.com/articles/about-sites/
Number plans
Genesys Cloud automatically provides default number plans; however, you can create a custom number plan.
Att,
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Breno Canyggia Ferreira Marreco
https://www.linkedin.com/in/brenocfm-40b62182/------------------------------