How do I set multiple values for checkbox properties?

When setting multiple values for a checkox property, the values should be separated with a semicolon (;).
'value1;value2;value5'

When updating a record through the Contacts API, the property value should be a single string with all of the values separated by semicolons:

{
    "property": "property_name",
    "value": "value1;value3;value4"
},

 

For the Forms API, make sure that the semicolons are also URL encoded:

...&property_name=value1%3Bvalue2%3Bvalue4