It cannot be used solely as a number.

example:
/give playername minecraft:activator_rail[minecraft:custom_name="1"] 

/give playername minecraft:activator_rail[minecraft:custom_name=" "] doesn't work either.

I don't know how to display the version so I'm writing it here.

24w09a 24w10a 24w11a 24w12a 24w13a 24w14a 1.20.5 Pre-Release 1 1.20.5 Pre-Release 2 1.20.5 Pre-Release 3 1.20.5 Pre-Release 4 1.20.5 Release Candidate 1 1.20.5 Release Candidate 2 1.20.5 Release Candidate 3 1.20.5 1.20.6 Release Candidate 1