bought ipad air 2 on ebay which has activation lock so can't enter my apple id

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Turn off Activation Lock – Apple Support

As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.

Sorry, but you’re short of options.

The All Too Common SAD Reality of Buying … - Apple Community

Ask the seller to remove the lock or give you a refund, or ask eBay for a refund.

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Return it for a refund, you will never be able to use it when it's Activation Locked.

Activation Lock is a theft deterrent feature with no bypass or workaround.

Without the owner's authorisation (Apple ID & password), no thief or anyone including you can re-use the device.