Meaning of ‘Throw in’ Phrasal Verb in English

When buying a new phone, they often throw in a complimentary case.

The car dealer decided to throw in a free warranty with the purchase.

The real estate agent might throw in some furniture to sweeten the deal.

The seller agreed to throw in free delivery for the large furniture purchase.

The package deal includes the hotel stay, and they may throw in a spa voucher.

As a promotion, the company decided to throw in a free sample for every purchase.