First, try restarting/rebooting your device. The time-honoured way to automagically fix many mysteriously inexplicable trivial software glitches. Maybe it'll help, maybe not, but it never hurts.
iPhones support a few image/media formats not supported by all Android phones.
Android phones support a few image/media formats not supported by iPhones.
Android phones sometimes support a few image/media formats not supported by other Android phones.
You can try installing a different Messaging App which supports more stuff (like more attachment formats), no need to use whatever default Messaging App came bundled with your phone's operating system. There's dozens to choose from on iOS or Android (or Windows, linux, etc), many are free, and most add functionality or features or cool bling which is lacking in their "plain vanilla" counterparts.
