While calling a « Run a Child Flow » from a Power Automate Flow, you could get an error about « InvokerConnectionOverrideFailed » and « header.X-MS-APIM-Tokens ».
After investigating, to resolve this issue you need to open the « details » view of your child flow, and click on the « Edit » button from the « Run only users » card:
Then in the Connections Used section, make sure to select « Use this connection (your_username@domain.com) » instead of the default « Provided by run-only user ». It will permit to run this child flow with your rights.