Robot.txt Unable to fetch & Crawl Status error.

My Search console shows host status error. Host had problem since last week. Inside host status robot.txt fetch shows high fail rate since last week . Also Server connectivity error is high recently. Can you help me to solve the issue?. This robots.txt fetch issue started from last month.Search console Indexing request rejected multiple times. Last day we updated robots.txt file and that fetched but today again shows the error.