I worked at Redworks B.V. company as a web developer position.
For front end development, Angular 9 was used, and for back end, php/perl are used.
Also, 3rd party APIs like Porta Billing, SIGNICAT, COIN, etc are integrated with our back end.
And I developed APIs using perl based on SOAP structure.
To implement the VoIP services like CDRs, IVR, etc, PortaBilling APIs are used mainly, and our APIs were also used.
Angular Material, bootstrap are used for front end development.