unable to pair ipencil to ipad air

If you have a third generation iPad Air, it is compatible with the first generation Apple Pencil. First and second generation iPad Air are not compatible.

Here is the full compatibility list:

Apple Pencil (2nd generation)

You can use Apple Pencil (2nd generation) with these iPad models: 

• iPad Pro 12.9-inch (3rd generation) and later
• iPad Pro 11-inch (1st generation) and later

Apple Pencil (1st generation)

You can use Apple Pencil (1st generation) with these iPad models:

• iPad Pro 12.9-inch (1st or 2nd generation)
• iPad Pro 10.5-inch
• iPad Pro 9.7-inch
• iPad Air (3rd generation)
• iPad (7th generation)
• iPad (6th generation)
• iPad mini (5th generation)

Not sure which iPad you have? Identify your iPad model.

If you do have an iPad Air3, ensure that you have updated your iPad to the most recent version of iPadOS - at time of writing, this is iPadOS 13.7. The most recent versions of iPadOS resolve a known issue with pairing and operation of the Apple Pencil with the iPad Air3.

Are you sure you have an iPad that is compatible with the pencil.

here is information from the Apple data:

Models that support Apple Pencil

The following models support Apple Pencil (2nd generation):

• iPad Pro 12.9-inch (3rd generation and later)
• 
  
• iPad Pro 11-inch

The following models support Apple Pencil (1st generation):

• iPad Pro 12.9-inch (1st and 2nd generation)
• 
  
• iPad Pro 10.5-inch
• 
  
• iPad Pro 9.7-inch
• 
  
• iPad Air (3rd generation)
• 
  
• iPad (6th generation and later)
• 
  
• iPad mini (5th generation)