Unlike other Android phones where you hold keys and then plug in the cable, Samsung devices often require the cable to be connected to a PC (or a charger, though PC is preferred) to trigger the mode properly. Connect your Galaxy A7 to your computer using the USB cable before pressing the button combination.
Connect your device to a desktop computer or laptop using a high-quality USB data cable. How to Open Fastboot Mode on SAMSUNG Galaxy A7 ...
on Samsung devices) on a Samsung Galaxy A7, follow these steps based on your specific model version. For Newer Models (A7 2018, A7 2020, Tab A7) Unlike other Android phones where you hold keys
This is the fastest way but requires root privileges which yourself may not have. on Samsung devices) on a Samsung Galaxy A7,
Here are the step-by-step methods to access the mode you might be calling "Fastboot Mode." These work for (A7 2015, A7 2016, A7 2017, A7 2018).