I have seen variations on this topic, but none recently and none with my particular issue. I have Message+ on my iPad for texting over Wi-Fi. Text and emojis works fine, but there is no support for sending gifs on Message+ as there is on the plain old Messages app on my Pixel 2. This seems more like a feature request than a support question. Why on earth does the Message+ app not support gifs?
You should be able to send GIFs on Messages+. We definitely want to take a closer look into this issue. We will be sending you a Private Note, so we can further assist you.
I actually found a way to do it, but it's much harder on the iPad app than it is on my phone:
1. Tap + icon next to message input
2. Tap Search
3. Enter Search criteria
4. Tap GIF on format selection bar
Now the GIFs appear.
On the phone there's an option to go right to GIFs from the keyboard.