how can i make a wither spawn with 1k health

i have a server with buffed monsters, it has monsters with several buffs and abilities. and the wither has 1k health. im recreating this server but the wither's health is not updating attribute @e[type=wither,limit=1] minecraft:max_health base set 1000 [This command is in chain, always active] data modify entity @e[type=wither,limit=1] Health set value 1000 [This command is chained to the previous command, always active] while this setup did and still does work on my previous server, it isn't working on the newer one. why?