I cut my teeth in the industry on the test side at MS; it was a bit adversarial with the dev side. And there was a third side to get us both on documentation.
It was frustrating but, I think we made Good Stuff (NT4, Win2k).
I love them, discovered when I lived in Seattle. Now I've got a crazy little one WJOP-LP but some of the DJs play local little bands and more obscure artists. Must be a teaching/training type thing.
We had this problem at work too. And didn't want yet another service provider. Built our own, in Go, for incoming and outgoing. Has some routing features too. Client Webhooks configs stored in that service and our main app API to that thing to configure.
Not optimized for scale, likely only a few thousand per second capable.