what i wrong coding Merge mob and item. can someone figured out pls ?

i was try to create this thing for 1 year, i have no one can help in my community. so, i am not good at English much 
here is the code

execute as @e[type=sheep] at @s run tag @s remove merge1

execute as @e[type=sheep,tag=!merge1,limit=1,sort=random] at @s run tag @s add merge1

execute as @e[type=sheep,tag=merge1,limit=1,sort=nearest] at @s run say Debug: @s has tag merge1

execute as @e[type=sheep,tag=merge1,limit=1,sort=nearest] at @s run tag @s add merge2

execute as @e[type=sheep,tag=merge2,limit=1,sort=nearest] at @s run say Debug: @s has tag merge2

execute as @e[type=sheep,tag=merge2,limit=1,sort=nearest,distance=..2] at @s run tag @s add merged

execute as @e[type=sheep,tag=merged,limit=1,sort=nearest] at @s run say Debug: @s has tag merged

execute as @e[type=sheep] at @s unless score @s nstacked matches 1.. run scoreboard players set @s nstacked 1

execute as @e[type=sheep,tag=merged] at @s run scoreboard players operation @s nstacked += @s nstacked

execute as @e[type=sheep,tag=merge2,scores={nstacked=..0}] at @s run kill @s

execute as @e[tag=merge1,scores={nstacked=1..64}] at @s run data merge entity @s {CustomNameVisible:1b,CustomName:'{"text":"", "extra":[{"score":{"name":"@s","objective":"nstacked"}},{"text":"x Entity"}]}'}
execute as @e[tag=merge1,scores={nstacked=65..}] at @s run data merge entity @s {CustomNameVisible:1b,CustomName:'{"text":"64+ x Entity"}'}

execute as @e[type=sheep,tag=merge2] run tag @s remove merge2

execute as @e[type=sheep,tag=merged] run tag @s remove merged

execute as @e[type=sheep,tag=merge1,scores={nstacked=2..}] run summon sheep ~ ~ ~ {nstacked=@s[nstacked]-1}

execute as @e[type=sheep,tag=merge1,scores={nstacked=2..}] run kill @s

in error is here :
execute as @e[type=sheep,tag=merge1,scores={nstacked=2..}] run summon sheep ~ ~ ~ {nstacked=@s[nstacked]-1}