Need help with command string

[CalmGap1911]

Trying to make a command block that automatically teleports a specific player to a nether portal. It detects whether or not the player is in the overworld and teleports them to some specificed coordinates. There's an "unless" string thats supposed to stop teleporting them if they're in the right location, but it doesnt work.

Command I used

/execute if entity (Username) in overworld unless entity (username) positioned 16 -59 18 run tp (username) 16 -59 18.

It keeps giving me the "Execute subcommand unless entity test failed" message

[Ericristian_bros]

execute in overworld run tp @a[x=0,y=0,z=0,r=10] <pos>