I have extra phone to use. Htc one m8. Is this ok to use as for mavic dji 4 app?

The answer is maybe, but you do so at your own risk.

Recommended Devices from http://www.dji.com/mavic/info#specs        

iOS 9.0 or later
Android 4.1.2 or later

ios: iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone 7, iPhone 7 Plus, iPod touch 6, iPad Pro, iPad Air, iPad Air Wi-Fi + Cellular, iPad mini 2, iPad mini 2 Wi-Fi + Cellular, iPad Air 2, iPad Air 2 Wi-Fi + Cellular, iPad mini 3, iPad mini 3 Wi-Fi + Cellular, iPad mini 4, and iPad mini 4 Wi-Fi + Cellular. This app is optimized for iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone 7 and iPhone 7 Plus.

Android: Samsung S7 edge, Samsung S7, Samsung S6, Samsung S5, Samsung NOTE4, Samsung NOTE3, Samsung tabs 705c, Ascend Mate 9, Ascend Mate 7, Huawei Honor 8, Huawei P8 Max, Vivo X7, Xiaomi 5, MI 3, Google Nexus 6p, Nexus 9, Google Nexus 7 II, LG V20, Sony Xperia Z3, Smartisan T1.
*Support for additional Android devices available as testing and development continues.

Use my M8 all the time, excellent control, no problems. I always put it in airplane mode first, then turn on GPS before loading Go. I use it to update MP to latest firmware as well. I wish all android phones were made as good as the HTC M series. I'm going to get the latest Ultra11 as soon as the price drops. I've also used an M9 successfully. Absolutely, definitely works. I have bought 5 different models for various family members and all work flawlessly. I am always fixing other people's (other brands) android phones - usually just OS/app problems or user confusion, so see many different brands of android out there. HTC has one of the most elegant and well thought out versions of android I've come across, it's like having a clean Google  phone with some really nice simple additions. Edit# I did have to get the upside-down plug small USB cable to connect to the RC. HTC's mini USB connector is upside down compared to most other Android phones, you'll notice this when normally charging the phone. You'll see it in the DJI store accessories. You can just use a slightly longer cable but not as neat. It's the cable that joins to the side of the RC.

Ex Machina Posted at 2017-6-7 15:42
The answer is maybe, but you do so at your own risk.

Recommended Devices from http://www.dji.com/mavic/info#specs        

ok, thanks!

Oglo Posted at 2017-6-7 15:46
Use my M8 all the time, excellent control, no problems. I always put it in airplane mode first, then turn on GPS before loading Go. I use it to update MP to latest firmware as well. I wish all android phones were made as good as the HTC M series. I'm going to get the latest Ultra11 as soon as the price drops. I've also used an M9 successfully. Absolutely, definitely works. I have bought 5 different models for various family members and all work flawlessly. I am always fixing other people's (other brands) android phones - usually just OS/app problems or user confusion, so see many different brands of android out there. HTC has one of the most elegant and well thought out versions of android I've come across, it's like having a clean Google  phone with some really nice simple additions. Edit# I did have to get the upside-down plug small USB cable to connect to the RC. HTC's mini USB connector is upside down compared to most other Android phones, you'll notice this when normally charging the phone. You'll see it in the DJI store accessories. You can just use a slightly longer cable but not as neat. It's the cable that joins to the side of the RC.

thanks you very much on your advise. i have 2 extra phones which is the M8 and iphone 5s... from the box of Mavic it says on the back "made for apple"... that why on my phantom 3 and mavic i tend to use the 5s,.. but ill put M8 in my option to use this., thanks for the out put!