Can’t set a wallpaper to my Apple Watch

Well, yeah, you can't set a wallpaper for an Apple Watch. It's not like you would be able to see it either way.

However, you can set a photo as your watch face. Bear in mind the instructions I am giving are for a Series 3 so there may be slight differences here and there. But here we go.

Setting it from the Apple Watch itself

Provided you have enough iCloud storage your photos should automatically back up to your Apple Watch. So, to set a specific picture as your watch face there are two options:

1. Go to the photos app on your Apple watch (click the digital crown and then navigate through it, should have similar icon to your phone). Then select a photo. Press the send button in the bottom right corner of the screen, then scroll down and click create watch face. Just like below, all the options appear to customize that face.
2. Alternatively, Press and hold until you can see the name of your watch face. Then swipe right and press new. Scroll down until you get to Photos. Then press add face. Then toggle all the settings e.g. tint, position of the actual time etc.

Setting it from the Apple Watch App on iPhone

Unlock your iPhone and find the Watch app. Then at the toolbar on the bottom, press Face Gallery. Scroll down to Photos. All of the options again for customizing the face will appear. Then scroll down to where it says content and click photos. Then choose the photo you want to set as your watch face and your done!

I really hope this helps :)