What it is
Error 135000 is a generic error from the WhatsApp Cloud API / Coexistence, without clear technical details from Meta.
Most common (observed) cause
Internal inconsistency in templates
Possible invalid or corrupted state of existing templates
Practical solution found by the community
✔ Delete ALL templates from the WABA (WhatsApp Business Account)
✔ Create them again from scratch
✔ Wait for Meta’s approval
✔ Test sending again
The expected result is that sending works correctly, but we’re not responsible if it doesn’t work for you.
After recreating the templates, the error is usually resolved and the API goes back to working normally.
Note
Solution based on recurring behavior in production, not officially documented by Meta.