Fix subscription request type

[KLewin23]

In the docs it states this is a number

[jamiecobbett]

In the schema we use to generate the types, this type can be one of:

- string
- integer
- 'null'

@KLewin23 "In the docs it states this is a number" could you provide a link to where you see this?

I've checked the template used to generate it and it has a bug around any multi-type field. I'll get that raised internally.