Maybe we have to work on the V2 and convert the code according to it. I found some info from Bandwidth about V1 vs V2 this might shed some light on the changes that we have to make:
V1 → V2 Messaging API Migration Guide
Key Differentiators First, let’s review the significant changes between the V1 Messaging API and V2 Messaging API and what this difference will look like in the API. Difference v1/messages v2/m...
support.bandwidth.com