From the official Php documentation :
Like any other PHP static variable, static properties may only be initialized using a literal or constant before PHP 5.6; expressions are not allowed. In PHP 5.6 and later, the same rules apply as const expressions: some limited expressions are possible, provided they can be evaluated at compile time.
So you cannot initialize a static variable with another variable. Replace $appdata['id'] with a constant string or remove the static attribute.
This is because all static declarations are resolved in compile-time, when the content of other variables is not known (see this other page of official doc).