I would like make an apple trade with my MacBook to buy an iPad

You can trade-in at a physical Apple Store, or using the online trade-in process:

Apple Trade In - Apple

Each device is assessed its own right. If using the online trade-in, you will be sent a shipping kit for each device. The device is returned using the shipping kit, assessed and if accepted a credit value is assigned. The trade-in value is returned to you by way of an Apple gift card device - and this can be used to purchase whatever you wish with Apple. 

Many choose to complete their trade-in in-store - as doing so removes any uncertainty as to the trade-in value or acceptance - and provides instant in-store credit against a purchase of your choice.

Trade it in for a gift card, and spend that on the iPad.

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