Error 135000 is a generic error from the WhatsApp Cloud API / Coexistence, without clear technical details from Meta.
Internal inconsistency in templates
Possible invalid or corrupted state of existing templates
Delete ALL templates from the WABA (WhatsApp Business Account)
Create them again from scratch
Wait for Meta’s approval
Test sending again
After recreating the templates, the error is usually resolved and the API goes back to working normally.
Solution based on recurring behavior in production, not officially documented by Meta.