I apologize, I assumed you where trying to send the video via attachment, not use the share option.
Here’s an easy way to test:
Download the video and try to attach it that way. If it sends, then the issue lies within the blink app. If it doesn’t, or it sets it from 1080p to SD (or worse), or prompts you to trim - it’s iMessage.
I don’t have an iPhone, but from my internet searches (thank God for Reddit), it appears that iOS with either drop the quality or just simply refuse to send it. I can’t find the exact specifications from Apple on size limitations.