# X_MCP_TENANT_REQUIRED

## Means

an MCP call names no tenant

## Typical cause

defineAppMcp({ tenant }) acts every call in the tenant the call names, and this call carries no tenant argument

## Fix

`list_tenants({}) — then send one of its values as the tenant argument of every tools/call`

[MCP and AI](/error-codes#mcp-and-ai)