Tier-2 General Visa Extension

My Tier-2 General visa will expire on 3rd June 2020. I requested my HR for new COS and got reply as below:

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We do not need to provide you with a restricted COS as you are already here in the UK working for us, you now need a general COS to support an extension.
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I got Visa extension information at :
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1- https://www.hr.admin.cam.ac.uk/hr-servi ... e/creating

2- https://www.gov.uk/tier-2-general/extend-your-visa

Tier 2 extensions
In order to apply for an extension to a Tier 2 (General) visa for a current University employee, a new CoS application will need to be submitted by the department/institution. Please note: the Compliance Team cannot process a CoS extension more than three months before an individual's Tier 2 visa is due to expire.
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I am bit confuse that whether I need new COS or same COS will work ?
This is for information that I am working with same company from beginning.

You need a NEW CoS. An Unrestricted CoS.

Thank you for your reply. For unrestricted cos, is there any salary constraint ? I can see below at https://workpermit.com/immigration/unit ... ponsorship:

Unrestricted Certificates of Sponsorship are to employ prospective employees who are already in the UK (except dependent family members of Tier 4 visa holders) or are outside of the UK and will be working in a role which pays £159,600 a year or more, or will be working in an inward investment post.

You simply need to meet the salary requirement stated in the SOC as relevant.