I work on a large C# platform that interops with a ton of vendor API's, the majority of which are also written in typed languages. The disjointed, loosely coupled nature of web systems is what causes problems. In particular, knowing what a "correct input" is to web systems is very difficult, where correct means:

1) Passes the API's immediate validation

2) Passes validation inside API's longer running processes

3) Passes business rules (it might be correct types, lengths etc, but fails anyway because of an incorrect combination of API calls)

Some of our vendors use Elixir, some use PHP, many use C# or Java. I really don't notice any significant difference between them on that account. The issues are all down to the complexity of the software and business requirements and that the whole thing is a giant distributed system.