In order for your ConfigEntry to be listed under your mod, it must meet this criteria:

1. The ConfigEntry is of type bool, int, or float
2. The field/property is static OR it's instanced under your entry class (className : BaseUnityPlugin)

By default, numerical entries have a range based on their default value:
min = -default * 2
max = default * 2

• If the default value is 0, the range will be -10 to 10)
• If the default value is between 0 and 1, the range will be -2 to 2)
• Precision will automatically be calculated for entries without attributes

If you want a customize this you can use the REPOConfigEntry attribute.

//bools can only have a custom name
[REPOConfigEntry("Enable")]
public static ConfigEntry<bool> toggle;

//ints can have a custom min/max
[REPOConfigEntry("Starting HP", min: 1, max: 100)]
public static ConfigEntry<int> startingHP;

//ints can also have a prefix/postfix for their label        
[REPOConfigEntry("USD", min: 1, max: 100, prefix:"$", postfix:"")]
public static ConfigEntry<int> money;

//ints can also display names instead of numbers
[REPOConfigEntry("Gamemode", "Creative", "Survival", "Spectator")]
public static ConfigEntry<int> gamemode;

//floats can have a min, max, precision (# of decimal points), prefix, postfix
[REPOConfigEntry("Speed", min: 1, max: 1000, precision: 2 postfix:" mph")]
public static ConfigEntry<float> speed;