The custom channel contactId (Custom ID) is currently capped at 50 characters. WhatsApp is moving from phone numbers to BSUIDs (Business Solution User IDs), which can exceed 50 characters. Customers who need to keep agent calls running through both WhatsApp and direct Twilio lines simultaneously cannot migrate their WhatsApp number directly into respond.io, and must instead pass the WhatsApp BSUID as the contactId. The 50-character limit makes this impossible and blocks preparation for the BSUID rollout.

Raise the contactId character limit to at least 150 characters, aligning with the maximum identifier length used by Twilio and WhatsApp.

During the WhatsApp BSUID transition, WhatsApp and direct Twilio call lines run in parallel. To route and identify contacts correctly across both, each contact's WhatsApp BSUID is passed into respond.io as the custom channel contactId. A 150-character limit allows the BSUID to fit, enabling the migration to complete without disrupting live agent operations.